Make CompositingReasonFinder a static class

This patch makes CompositingReasonFinder a static class (all functions
static) because there is no state that needs to be tracked. This is
just a simplification of the code and should not have any functional
change.

Bug: 915372
Change-Id: I39242f8de43705e3ccc61ae2ff9bb10d410b1823
Reviewed-on: https://chromium-review.googlesource.com/c/1381259
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617597}

diff --git a/third_party/blink/renderer/core/paint/compositing/compositing_inputs_updater.cc b/third_party/blink/renderer/core/paint/compositing/compositing_inputs_updater.cc
index 0c7bdf6..23841cd 100644
--- a/third_party/blink/renderer/core/paint/compositing/compositing_inputs_updater.cc
+++ b/third_party/blink/renderer/core/paint/compositing/compositing_inputs_updater.cc

@@ -24,12 +24,8 @@
              : clip_chain_parent->ClippingContainer();
 }
 
-CompositingInputsUpdater::CompositingInputsUpdater(
-    PaintLayer* root_layer,
-    CompositingReasonFinder& compositing_reason_finder)
-    : geometry_map_(kUseTransforms),
-      root_layer_(root_layer),
-      compositing_reason_finder_(compositing_reason_finder) {}
+CompositingInputsUpdater::CompositingInputsUpdater(PaintLayer* root_layer)
+    : geometry_map_(kUseTransforms), root_layer_(root_layer) {}
 
 CompositingInputsUpdater::~CompositingInputsUpdater() = default;
 
@@ -229,8 +225,8 @@
        layer->AncestorScrollingLayer()->NeedsCompositedScrolling());
 
   layer->SetPotentialCompositingReasonsFromNonStyle(
-      compositing_reason_finder_.NonStyleDeterminedDirectReasons(
-          layer, ignore_lcd_text));
+      CompositingReasonFinder::NonStyleDeterminedDirectReasons(
+          *layer, ignore_lcd_text));
 
   if (layer->GetScrollableArea()) {
     layer->GetScrollableArea()->UpdateNeedsCompositedScrolling(

diff --git a/third_party/blink/renderer/core/paint/compositing/compositing_inputs_updater.h b/third_party/blink/renderer/core/paint/compositing/compositing_inputs_updater.h
index 823f156..8510932 100644
--- a/third_party/blink/renderer/core/paint/compositing/compositing_inputs_updater.h
+++ b/third_party/blink/renderer/core/paint/compositing/compositing_inputs_updater.h

@@ -11,15 +11,12 @@
 namespace blink {
 
 class PaintLayer;
-class CompositingReasonFinder;
 
 class CompositingInputsUpdater {
   STACK_ALLOCATED();
 
  public:
-  explicit CompositingInputsUpdater(
-      PaintLayer* root_layer,
-      CompositingReasonFinder& compositing_reason_finder);
+  explicit CompositingInputsUpdater(PaintLayer* root_layer);
   ~CompositingInputsUpdater();
 
   void Update();
@@ -71,7 +68,6 @@
 
   LayoutGeometryMap geometry_map_;
   PaintLayer* root_layer_;
-  CompositingReasonFinder& compositing_reason_finder_;
 };
 
 }  // namespace blink

diff --git a/third_party/blink/renderer/core/paint/compositing/compositing_reason_finder.cc b/third_party/blink/renderer/core/paint/compositing/compositing_reason_finder.cc
index ea2e307..2ce4934 100644
--- a/third_party/blink/renderer/core/paint/compositing/compositing_reason_finder.cc
+++ b/third_party/blink/renderer/core/paint/compositing/compositing_reason_finder.cc

@@ -19,48 +19,42 @@
 
 namespace blink {
 
-CompositingReasonFinder::CompositingReasonFinder(LayoutView& layout_view)
-    : layout_view_(layout_view) {}
-
-bool CompositingReasonFinder::IsMainFrame() const {
-  return layout_view_.GetDocument().IsInMainFrame();
-}
-
 CompositingReasons CompositingReasonFinder::DirectReasons(
-    const PaintLayer* layer,
-    bool ignore_lcd_text) const {
+    const PaintLayer& layer,
+    bool ignore_lcd_text) {
   if (RuntimeEnabledFeatures::CompositeAfterPaintEnabled())
     return CompositingReason::kNone;
 
-  DCHECK_EQ(PotentialCompositingReasonsFromStyle(layer->GetLayoutObject()),
-            layer->PotentialCompositingReasonsFromStyle());
+  DCHECK_EQ(PotentialCompositingReasonsFromStyle(layer.GetLayoutObject()),
+            layer.PotentialCompositingReasonsFromStyle());
   CompositingReasons style_determined_direct_compositing_reasons =
-      layer->PotentialCompositingReasonsFromStyle() &
+      layer.PotentialCompositingReasonsFromStyle() &
       CompositingReason::kComboAllDirectStyleDeterminedReasons;
 
   return style_determined_direct_compositing_reasons |
          NonStyleDeterminedDirectReasons(layer, ignore_lcd_text);
 }
 
-bool CompositingReasonFinder::RequiresCompositingForScrollableFrame() const {
+bool CompositingReasonFinder::RequiresCompositingForScrollableFrame(
+    const LayoutView& layout_view) {
   // Need this done first to determine overflow.
-  DCHECK(!layout_view_.NeedsLayout());
-  if (IsMainFrame())
+  DCHECK(!layout_view.NeedsLayout());
+  if (layout_view.GetDocument().IsInMainFrame())
     return false;
 
-  const auto& settings = *layout_view_.GetDocument().GetSettings();
+  const auto& settings = *layout_view.GetDocument().GetSettings();
   if (!settings.GetPreferCompositingToLCDTextEnabled())
     return false;
 
-  if (layout_view_.GetFrameView()->Size().IsEmpty())
+  if (layout_view.GetFrameView()->Size().IsEmpty())
     return false;
 
-  return layout_view_.GetFrameView()->LayoutViewport()->ScrollsOverflow();
+  return layout_view.GetFrameView()->LayoutViewport()->ScrollsOverflow();
 }
 
 CompositingReasons
 CompositingReasonFinder::PotentialCompositingReasonsFromStyle(
-    LayoutObject& layout_object) const {
+    const LayoutObject& layout_object) {
   if (RuntimeEnabledFeatures::CompositeAfterPaintEnabled())
     return CompositingReason::kNone;
 
@@ -137,35 +131,35 @@
 }
 
 CompositingReasons CompositingReasonFinder::NonStyleDeterminedDirectReasons(
-    const PaintLayer* layer,
-    bool ignore_lcd_text) const {
+    const PaintLayer& layer,
+    bool ignore_lcd_text) {
   CompositingReasons direct_reasons = CompositingReason::kNone;
-  LayoutObject& layout_object = layer->GetLayoutObject();
+  LayoutObject& layout_object = layer.GetLayoutObject();
 
   // TODO(chrishtr): remove this hammer in favor of something more targeted.
   // See crbug.com/749349.
-  if (layer->ClipParent() && layer->GetLayoutObject().IsOutOfFlowPositioned())
+  if (layer.ClipParent() && layer.GetLayoutObject().IsOutOfFlowPositioned())
     direct_reasons |= CompositingReason::kOutOfFlowClipping;
 
-  if (RequiresCompositingForRootScroller(*layer))
+  if (RequiresCompositingForRootScroller(layer))
     direct_reasons |= CompositingReason::kRootScroller;
 
   // Composite |layer| if it is inside of an ancestor scrolling layer, but that
   // scrolling layer is not on the stacking context ancestor chain of |layer|.
   // See the definition of the scrollParent property in Layer for more detail.
-  if (const PaintLayer* scrolling_ancestor = layer->AncestorScrollingLayer()) {
-    if (scrolling_ancestor->NeedsCompositedScrolling() && layer->ScrollParent())
+  if (const PaintLayer* scrolling_ancestor = layer.AncestorScrollingLayer()) {
+    if (scrolling_ancestor->NeedsCompositedScrolling() && layer.ScrollParent())
       direct_reasons |= CompositingReason::kOverflowScrollingParent;
   }
 
-  if (RequiresCompositingForScrollDependentPosition(*layer, ignore_lcd_text))
+  if (RequiresCompositingForScrollDependentPosition(layer, ignore_lcd_text))
     direct_reasons |= CompositingReason::kScrollDependentPosition;
 
   // TODO(crbug.com/839341): Remove once we support main-thread AnimationWorklet
   // and don't need to promote the scroll-source.
-  if (layer->GetScrollableArea() && layer->GetLayoutObject().GetNode() &&
+  if (layer.GetScrollableArea() && layer.GetLayoutObject().GetNode() &&
       ScrollTimeline::HasActiveScrollTimeline(
-          layer->GetLayoutObject().GetNode())) {
+          layer.GetLayoutObject().GetNode())) {
     direct_reasons |= CompositingReason::kScrollTimelineTarget;
   }
 
@@ -173,12 +167,13 @@
   // PaintLayer children and whose children can't use its backing to render
   // into. These children (the controls) always need to be promoted into their
   // own layers to draw on top of the accelerated video.
-  if (layer->CompositingContainer() &&
-      layer->CompositingContainer()->GetLayoutObject().IsVideo())
+  if (layer.CompositingContainer() &&
+      layer.CompositingContainer()->GetLayoutObject().IsVideo())
     direct_reasons |= CompositingReason::kVideoOverlay;
 
-  if (layer->IsRootLayer() && (RequiresCompositingForScrollableFrame() ||
-                               layout_view_.GetFrame()->IsLocalRoot())) {
+  if (layer.IsRootLayer() &&
+      (RequiresCompositingForScrollableFrame(*layout_object.View()) ||
+       layout_object.GetFrame()->IsLocalRoot())) {
     direct_reasons |= CompositingReason::kRoot;
   }
 

diff --git a/third_party/blink/renderer/core/paint/compositing/compositing_reason_finder.h b/third_party/blink/renderer/core/paint/compositing/compositing_reason_finder.h
index 87c3b37..4df36f7b 100644
--- a/third_party/blink/renderer/core/paint/compositing/compositing_reason_finder.h
+++ b/third_party/blink/renderer/core/paint/compositing/compositing_reason_finder.h

@@ -21,23 +21,22 @@
   DISALLOW_NEW();
 
  public:
-  explicit CompositingReasonFinder(LayoutView&);
+  static CompositingReasons PotentialCompositingReasonsFromStyle(
+      const LayoutObject&);
 
-  CompositingReasons PotentialCompositingReasonsFromStyle(LayoutObject&) const;
+  static CompositingReasons NonStyleDeterminedDirectReasons(
+      const PaintLayer&,
+      bool ignore_lcd_text);
 
-  CompositingReasons NonStyleDeterminedDirectReasons(
-      const PaintLayer*,
-      bool ignore_lcd_text) const;
-  LayoutView& layout_view_;
   DISALLOW_COPY_AND_ASSIGN(CompositingReasonFinder);
 
   // Returns the direct reasons for compositing the given layer. If
   // |ignoreLCDText| is true promotion will not try to preserve subpixel text
   // rendering (i.e. partially transparent layers will be promoted).
-  CompositingReasons DirectReasons(const PaintLayer*,
-                                   bool ignore_lcd_text) const;
+  static CompositingReasons DirectReasons(const PaintLayer&,
+                                          bool ignore_lcd_text);
 
-  bool RequiresCompositingForScrollableFrame() const;
+  static bool RequiresCompositingForScrollableFrame(const LayoutView&);
   static CompositingReasons CompositingReasonsForAnimation(
       const ComputedStyle&);
   static bool RequiresCompositingForOpacityAnimation(const ComputedStyle&);
@@ -51,9 +50,6 @@
   static bool RequiresCompositingForScrollDependentPosition(
       const PaintLayer&,
       bool ignore_lcd_text);
-
- private:
-  bool IsMainFrame() const;
 };
 
 }  // namespace blink

diff --git a/third_party/blink/renderer/core/paint/compositing/compositing_requirements_updater.cc b/third_party/blink/renderer/core/paint/compositing/compositing_requirements_updater.cc
index aa75b8fac..03f3fc5 100644
--- a/third_party/blink/renderer/core/paint/compositing/compositing_requirements_updater.cc
+++ b/third_party/blink/renderer/core/paint/compositing/compositing_requirements_updater.cc

@@ -210,15 +210,8 @@
 }
 
 CompositingRequirementsUpdater::CompositingRequirementsUpdater(
-    LayoutView& layout_view,
-    CompositingReasonFinder& compositing_reason_finder)
-    : layout_view_(layout_view)
-#if DCHECK_IS_ON()
-      ,
-      compositing_reason_finder_(compositing_reason_finder)
-#endif
-{
-}
+    LayoutView& layout_view)
+    : layout_view_(layout_view) {}
 
 CompositingRequirementsUpdater::~CompositingRequirementsUpdater() = default;
 
@@ -317,12 +310,12 @@
 #if DCHECK_IS_ON()
   if (layer_can_be_composited) {
     DCHECK(direct_from_paint_layer ==
-           compositing_reason_finder_.DirectReasons(
-               layer,
+           CompositingReasonFinder::DirectReasons(
+               *layer,
                ignore_lcd_text || moves_with_respect_to_compositing_ancestor))
         << " Expected: "
         << CompositingReason::ToString(
-               compositing_reason_finder_.DirectReasons(layer, ignore_lcd_text))
+               CompositingReasonFinder::DirectReasons(*layer, ignore_lcd_text))
         << " Actual: " << CompositingReason::ToString(direct_from_paint_layer);
   }
 #endif

diff --git a/third_party/blink/renderer/core/paint/compositing/compositing_requirements_updater.h b/third_party/blink/renderer/core/paint/compositing/compositing_requirements_updater.h
index 2b4bd5e7..81b6e85 100644
--- a/third_party/blink/renderer/core/paint/compositing/compositing_requirements_updater.h
+++ b/third_party/blink/renderer/core/paint/compositing/compositing_requirements_updater.h

@@ -34,7 +34,6 @@
 
 namespace blink {
 
-class CompositingReasonFinder;
 class PaintLayer;
 class LayoutView;
 
@@ -42,7 +41,7 @@
   STACK_ALLOCATED();
 
  public:
-  CompositingRequirementsUpdater(LayoutView&, CompositingReasonFinder&);
+  CompositingRequirementsUpdater(LayoutView&);
   ~CompositingRequirementsUpdater();
 
   //  Recurse through the layers in z-index and overflow order (which is
@@ -72,9 +71,6 @@
                        CompositingReasonsStats&);
 
   LayoutView& layout_view_;
-#if DCHECK_IS_ON()
-  CompositingReasonFinder& compositing_reason_finder_;
-#endif
 };
 
 }  // namespace blink

diff --git a/third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.cc b/third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.cc
index 8748e94..06fff3d 100644
--- a/third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.cc
+++ b/third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.cc

@@ -68,7 +68,6 @@
 
 PaintLayerCompositor::PaintLayerCompositor(LayoutView& layout_view)
     : layout_view_(layout_view),
-      compositing_reason_finder_(layout_view),
       pending_update_type_(kCompositingUpdateNone),
       has_accelerated_compositing_(true),
       compositing_(false),
@@ -132,7 +131,8 @@
   if (!has_accelerated_compositing_)
     return false;
   return layout_view_.GetFrame()->IsLocalRoot() ||
-         compositing_reason_finder_.RequiresCompositingForScrollableFrame();
+         CompositingReasonFinder::RequiresCompositingForScrollableFrame(
+             layout_view_);
 }
 
 void PaintLayerCompositor::UpdateAcceleratedCompositingSettings() {
@@ -366,7 +366,7 @@
   DCHECK(!HasAcceleratedCompositing());
 
   if (update_type >= kCompositingUpdateAfterCompositingInputChange)
-    CompositingInputsUpdater(RootLayer(), compositing_reason_finder_).Update();
+    CompositingInputsUpdater(RootLayer()).Update();
 
 #if DCHECK_IS_ON()
   CompositingInputsUpdater::AssertNeedsCompositingInputsUpdateBitsCleared(
@@ -452,7 +452,7 @@
   Vector<PaintLayer*> layers_needing_paint_invalidation;
 
   if (update_type >= kCompositingUpdateAfterCompositingInputChange) {
-    CompositingInputsUpdater(update_root, compositing_reason_finder_).Update();
+    CompositingInputsUpdater(update_root).Update();
 
 #if DCHECK_IS_ON()
     // FIXME: Move this check to the end of the compositing update.
@@ -470,7 +470,7 @@
       return;
     }
 
-    CompositingRequirementsUpdater(layout_view_, compositing_reason_finder_)
+    CompositingRequirementsUpdater(layout_view_)
         .Update(update_root, compositing_reasons_stats);
 
     CompositingLayerAssigner layer_assigner(this);
@@ -782,9 +782,9 @@
 
 void PaintLayerCompositor::UpdatePotentialCompositingReasonsFromStyle(
     PaintLayer& layer) {
-  layer.SetPotentialCompositingReasonsFromStyle(
-      compositing_reason_finder_.PotentialCompositingReasonsFromStyle(
-          layer.GetLayoutObject()));
+  auto reasons = CompositingReasonFinder::PotentialCompositingReasonsFromStyle(
+      layer.GetLayoutObject());
+  layer.SetPotentialCompositingReasonsFromStyle(reasons);
 }
 
 bool PaintLayerCompositor::CanBeComposited(const PaintLayer* layer) const {
@@ -795,7 +795,7 @@
     return false;
 
   const bool has_compositor_animation =
-      compositing_reason_finder_.CompositingReasonsForAnimation(
+      CompositingReasonFinder::CompositingReasonsForAnimation(
           *layer->GetLayoutObject().Style()) != CompositingReason::kNone;
   return has_accelerated_compositing_ &&
          (has_compositor_animation || !layer->SubtreeIsInvisible()) &&

diff --git a/third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.h b/third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.h
index 92fdf8f..52f4f7f 100644
--- a/third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.h
+++ b/third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.h

@@ -200,8 +200,6 @@
 
   LayoutView& layout_view_;
 
-  CompositingReasonFinder compositing_reason_finder_;
-
   CompositingUpdateType pending_update_type_;
 
   bool has_accelerated_compositing_;