Implement DisplayList GatherPixelRefs

cc/BUILD.gn

Index: cc/BUILD.gn
diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 8c695e55483bfa331500286eb0186908f53d9a41..dca1addf9e8f74029a7f894977f63ac4f84ac437 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn
@@ -573,6 +573,7 @@ source_set("test_support") {
     "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 @@ test("cc_unittests") {
     "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 @@ test("cc_unittests") {
     "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",