Implement DisplayList GatherPixelRefs

Take advantage of DisplayList playing back to generate SkPicture, and
use existing functions that gathers pixel ref from a single SkPicture.

R=ajuma, enne, vmpstr
BUG=440468, 472590

Committed: https://crrev.com/3d69b19b57904847ffec31b0f5d4f3568b5c6f35
Cr-Commit-Position: refs/heads/master@{#323152}

Review URL: https://codereview.chromium.org/1045953002

Cr-Commit-Position: refs/heads/master@{#323631}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 8c695e5..dca1add 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -573,6 +573,7 @@
     "test/fake_delegated_renderer_layer.h",
     "test/fake_delegated_renderer_layer_impl.cc",
     "test/fake_delegated_renderer_layer_impl.h",
+    "test/fake_display_list_recording_source.h",
     "test/fake_external_begin_frame_source.cc",
     "test/fake_external_begin_frame_source.h",
     "test/fake_impl_proxy.h",
@@ -791,6 +792,7 @@
     "quads/list_container_unittest.cc",
     "quads/render_pass_unittest.cc",
     "resources/display_item_list_unittest.cc",
+    "resources/display_list_recording_source_unittest.cc",
     "resources/layer_quad_unittest.cc",
     "resources/picture_layer_tiling_set_unittest.cc",
     "resources/picture_layer_tiling_unittest.cc",
@@ -800,6 +802,7 @@
     "resources/pixel_ref_map_unittest.cc",
     "resources/platform_color_unittest.cc",
     "resources/prioritized_resource_unittest.cc",
+    "resources/recording_source_unittest.cc",
     "resources/resource_provider_unittest.cc",
     "resources/resource_update_controller_unittest.cc",
     "resources/scoped_gpu_raster_unittest.cc",