Animations: Implement runtime flag for enabling compositor animation timelines.

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index c01231ece0675a9256bef05c8322dde5a74d07c6..af9edfc758c46c257a74552ab198abcbc3d8aa16 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -216,6 +216,10 @@ void RenderWidgetCompositor::Initialize() {
     settings.record_full_layer =
         !blink::WebRuntimeFeatures::slimmingPaintDisplayItemCacheEnabled();
   }
+  if (cmd->HasSwitch(switches::kEnableCompositorAnimationTimelines)) {
+    settings.use_compositor_animation_timelines = true;
+    blink::WebRuntimeFeatures::enableCompositorAnimationTimelines(true);
+  }
 
   settings.default_tile_size = CalculateDefaultTileSize();
   if (cmd->HasSwitch(switches::kDefaultTileWidth)) {