Revert of Revert of Implement DisplayList GatherPixelRefs

cc/BUILD.gn

Index: cc/BUILD.gn
diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 5354b7c2ce476b2382822c4e785a6170e0375c9c..2d4a39330073a7067955e2afdebbd86d71d4a9c7 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn
@@ -570,6 +570,7 @@
     "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",
@@ -789,6 +790,7 @@
     "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",
@@ -798,6 +800,7 @@
     "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",