Reland "Add quick app barebones UI implementation"

This is a reland of commit 78f47a099ad0260751a4ac28f844d8c12d71f72c

The ASAN failure was caused by QuickAppAccessModel getting destroyed
before the HomeButton which is observing it. Resetting
quick_app_model_observation_ in OnShellDestroying() ensures that the
QuickAppAccessModel still exists when removing the homebutton as
observer.

Original change's description:
> Add quick app barebones UI implementation
>
> Add quick app button to be shown next to the home button. Quick app can
> be set by passing an app_id to the app list controller function
> SetHomeButtonQuickApp(). The home button will observe the new
> QuickAppAccessModel for the quick app to be changed and will then show
> the quick app button.
>
> Animations, icon loading, and additional metric to be added in follow
> ups.
>
> Bug=b:266734005
>
> Change-Id: I2840998e5860ab33a1607022417a55277e06d660
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4380277
> Commit-Queue: Matthew Mourgos <mmourgos@chromium.org>
> Reviewed-by: Toni Barzic <tbarzic@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1126186}

Change-Id: I87c713c91b1b098ea21b99a57bf9612129754c55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4401631
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Commit-Queue: Matthew Mourgos <mmourgos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1126712}

diff --git a/ash/shelf/home_button.h b/ash/shelf/home_button.h
index 90d088a..1ce809f1 100644
--- a/ash/shelf/home_button.h
+++ b/ash/shelf/home_button.h

@@ -8,16 +8,22 @@
 #include <memory>
 
 #include "ash/app_list/app_list_metrics.h"
+#include "ash/app_list/app_list_model_provider.h"
+#include "ash/app_list/quick_app_access_model.h"
 #include "ash/ash_export.h"
+#include "ash/public/cpp/app_list/app_list_controller_observer.h"
 #include "ash/shelf/home_button_controller.h"
 #include "ash/shelf/shelf_button_delegate.h"
 #include "ash/shelf/shelf_control_button.h"
+#include "ash/shell_observer.h"
+#include "base/scoped_observation.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/views/view_targeter_delegate.h"
 
 namespace views {
 class AnimationBuilder;
 class CircleLayerDelegate;
+class ImageButton;
 class Label;
 }  // namespace views
 
@@ -30,6 +36,7 @@
 class Shelf;
 class ShelfButtonDelegate;
 class ShelfNavigationWidget;
+class Shell;
 
 // Button used for the AppList icon on the shelf. It opens the app list (in
 // clamshell mode) or home screen (in tablet mode). Because the clamshell-mode
@@ -40,7 +47,10 @@
 // launch Assistant.
 class ASH_EXPORT HomeButton : public ShelfControlButton,
                               public ShelfButtonDelegate,
-                              public views::ViewTargeterDelegate {
+                              public views::ViewTargeterDelegate,
+                              public ShellObserver,
+                              public AppListModelProvider::Observer,
+                              public QuickAppAccessModel::Observer {
  public:
   class ScopedNoClipRect {
    public:
@@ -126,7 +136,15 @@
   void AddNudgeAnimationObserverForTest(NudgeAnimationObserver* observer);
   void RemoveNudgeAnimationObserverForTest(NudgeAnimationObserver* observer);
 
-  views::View* label_container_for_test() const { return label_container_; }
+  views::View* expandable_container_for_test() const {
+    return expandable_container_;
+  }
+
+  views::Label* nudge_label_for_test() const { return nudge_label_; }
+
+  views::ImageButton* quick_app_button_for_test() const {
+    return quick_app_button_;
+  }
 
  protected:
   // views::Button:
@@ -137,6 +155,16 @@
   // Creates `nudge_label_` for launcher nudge.
   void CreateNudgeLabel();
 
+  // Creates the `expandable_container_` which holds either the `nudge_label_`
+  // or the `quick_app_button_`.
+  void CreateExpandableContainer();
+
+  // Creates the `quick_app_button_` to be shown next to the home button.
+  void CreateQuickAppButton();
+
+  // Called when the quick app button is pressed.
+  void QuickAppButtonPressed();
+
   // Animation functions for launcher nudge.
   void AnimateNudgeRipple(views::AnimationBuilder& builder);
   void AnimateNudgeBounce(views::AnimationBuilder& builder);
@@ -157,6 +185,24 @@
   bool DoesIntersectRect(const views::View* target,
                          const gfx::Rect& rect) const override;
 
+  // ShellObserver:
+  void OnShellDestroying() override;
+
+  // AppListModelProvider::Observer:
+  void OnActiveAppListModelsChanged(AppListModel* model,
+                                    SearchModel* search_model) override;
+
+  // QuickAppAccessModel::Observer:
+  void OnQuickAppChanged() override;
+
+  base::ScopedObservation<QuickAppAccessModel, QuickAppAccessModel::Observer>
+      quick_app_model_observation_{this};
+
+  base::ScopedObservation<Shell, ShellObserver> shell_observation_{this};
+
+  base::ScopedObservation<AppListModelProvider, AppListModelProvider::Observer>
+      app_list_model_observation_{this};
+
   Shelf* const shelf_;
 
   // The controller used to determine the button's behavior.
@@ -169,9 +215,10 @@
   // The label view and for launcher nudge animation.
   views::Label* nudge_label_ = nullptr;
 
-  // The container of `nudge_label_`. This is also responsible for painting the
-  // background of the label.
-  views::View* label_container_ = nullptr;
+  // The container of `nudge_label_` or `quick_app_button_`. This is also
+  // responsible for painting the background of the contents. This container can
+  // expand visually by animation.
+  views::View* expandable_container_ = nullptr;
 
   // The timer that counts down to hide the nudge_label_ from showing state.
   base::OneShotTimer label_nudge_timer_;
@@ -182,6 +229,13 @@
 
   std::unique_ptr<ScopedNoClipRect> scoped_no_clip_rect_;
 
+  // The app button which is shown next to the home button. Only shown when
+  // set by SetQuickApp().
+  views::ImageButton* quick_app_button_ = nullptr;
+
+  // The app_id of the quick app button.
+  std::string quick_app_id_;
+
   base::ObserverList<NudgeAnimationObserver> observers_;
 
   base::WeakPtrFactory<HomeButton> weak_ptr_factory_{this};