CC Animations: Make LayerAnimationController creation optional

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index c50f9efdddb5321b6095e8c8a8bf4b64482433b9..31219c6ff0f3ddda16d8f82c04c7972da7c93a1b 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -81,11 +81,20 @@ Compositor::Compositor(gfx::AcceleratedWidget widget,
       compositor_lock_(NULL),
       layer_animator_collection_(this),
       weak_ptr_factory_(this) {
-  root_web_layer_ = cc::Layer::Create();
-
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
 
   cc::LayerTreeSettings settings;
+
+  cc::LayerSettings ui_layer_settings;
+  if (command_line->HasSwitch(
+          switches::kUIEnableCompositorAnimationTimelines)) {
+    settings.hud_layer_settings_.use_compositor_animation_timelines = true;
+    ui_layer_settings.use_compositor_animation_timelines = true;
+  }
+  Layer::SetUILayerSettings(ui_layer_settings);
+
+  root_web_layer_ = cc::Layer::Create(Layer::UILayerSettings());
+
   // When impl-side painting is enabled, this will ensure PictureLayers always
   // can have LCD text, to match the previous behaviour with ContentLayers,
   // where LCD-not-allowed notifications were ignored.
@@ -135,9 +144,6 @@ Compositor::Compositor(gfx::AcceleratedWidget widget,
   // raster threads.
   settings.gather_pixel_refs = false;
 
-  settings.use_compositor_animation_timelines =
-      command_line->HasSwitch(switches::kUIEnableCompositorAnimationTimelines);
-
   base::TimeTicks before_create = base::TimeTicks::Now();
   host_ = cc::LayerTreeHost::CreateSingleThreaded(
       this, this, context_factory_->GetSharedBitmapManager(),
@@ -162,7 +168,7 @@ Compositor::~Compositor() {
   DCHECK(begin_frame_observer_list_.empty());
 
   if (root_layer_)
-    root_layer_->SetCompositor(NULL);
+    root_layer_->ResetCompositor();
 
   // Stop all outstanding draws before telling the ContextFactory to tear
   // down any contexts that the |host_| may rely upon.
@@ -184,13 +190,11 @@ void Compositor::SetRootLayer(Layer* root_layer) {
   if (root_layer_ == root_layer)
     return;
   if (root_layer_)
-    root_layer_->SetCompositor(NULL);
+    root_layer_->ResetCompositor();
   root_layer_ = root_layer;
-  if (root_layer_ && !root_layer_->GetCompositor())
-    root_layer_->SetCompositor(this);
   root_web_layer_->RemoveAllChildren();
   if (root_layer_)
-    root_web_layer_->AddChild(root_layer_->cc_layer());
+    root_layer_->SetCompositor(this, root_web_layer_);
 }
 
 void Compositor::SetHostHasTransparentBackground(