Animations: Implement runtime flag for enabling compositor animation timelines.

cc/trees/layer_tree_settings.cc

Index: cc/trees/layer_tree_settings.cc
diff --git a/cc/trees/layer_tree_settings.cc b/cc/trees/layer_tree_settings.cc
index 09314adc577a5089561dabc012878b66eccaec66..998c37fbb94c9c1aecdb9bb9f832b18366db899d 100644
--- a/cc/trees/layer_tree_settings.cc
+++ b/cc/trees/layer_tree_settings.cc
@@ -71,7 +71,8 @@ LayerTreeSettings::LayerTreeSettings()
       record_full_layer(false),
       use_display_lists(false),
       verify_property_trees(false),
-      gather_pixel_refs(false) {
+      gather_pixel_refs(false),
+      use_compositor_animation_timelines(false) {
 }
 
 LayerTreeSettings::~LayerTreeSettings() {}