CC Animations: Make LayerAnimationController creation optional

ui/compositor/layer_animation_element.cc

Index: ui/compositor/layer_animation_element.cc
diff --git a/ui/compositor/layer_animation_element.cc b/ui/compositor/layer_animation_element.cc
index 9a528e5509a553bc153c66a9011464bcc5ad9aff..962533d0ce63423ac17a78b8e6460fa98d36e62b 100644
--- a/ui/compositor/layer_animation_element.cc
+++ b/ui/compositor/layer_animation_element.cc
@@ -340,7 +340,7 @@ class ThreadedLayerAnimationElement : public LayerAnimationElement {
     if (t < 1.0)
       return false;
 
-    if (Started()) {
+    if (Started() && IsThreaded()) {

[piman, 2015/04/29 00:46:11]

We don't use the thread in the UI compositor any more. Do we need support for
all this?

[loyso (OOO), 2015/04/29 01:30:39]

AFAIK, despite the fact that we don't use the thread in the UI compositor, we
still use the whole compositor infrastructure (LayerTreeHost/LayerTreeHostImpl
objects with SingleThreadProxy between them).

Apart from that, IsThreaded is defined as:
  bool IsThreaded() const override { return (duration() != base::TimeDelta()); }

Simply speaking, it doesn't pass 0-time anymations to the CC-compositor code
(which is started in SingleThreadProxy mode).

That's just a poor naming.
  // Whether this element animates on the compositor thread.
  virtual bool IsThreaded() const;

       delegate->RemoveThreadedAnimation(animation_id());
     }
 
@@ -349,14 +349,14 @@ class ThreadedLayerAnimationElement : public LayerAnimationElement {
   }
 
   void OnAbort(LayerAnimationDelegate* delegate) override {
-    if (delegate && Started()) {
+    if (delegate && Started() && IsThreaded()) {
       delegate->RemoveThreadedAnimation(animation_id());
     }
   }
 
   void RequestEffectiveStart(LayerAnimationDelegate* delegate) override {
     DCHECK(animation_group_id());
-    if (duration() == base::TimeDelta()) {
+    if (!IsThreaded()) {
       set_effective_start_time(requested_start_time());
       return;
     }