compositor: Tick the UI animations from cc, instead of from timer callbacks.

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index cfa02f27f7e64d399f7af7e887b17c1ed8e21037..f0998117d9d45310354033fd84c05fa320508a61 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -159,6 +159,11 @@ void Layer::Add(Layer* child) {
   child->OnDeviceScaleFactorChanged(device_scale_factor_);
   if (GetCompositor())
     child->SendPendingThreadedAnimations();
+  if (child->GetAnimator() && child->GetAnimator()->is_animating()) {

[piman, 2014/05/23 21:38:56]

nit: GetAnimator() is non-trivial:
1- can we call it once and keep the return value?
2- it also has a side effect of creating the animator. Doesn't that mean we'll
create a LayerAnimator for every layer, even though it may never be animated?

Actually, GetAnimator() says that it never returns NULL.

[sadrul, 2014/05/23 21:56:11]

Done. Added Layer::IsAnimating() const { return animator_ &&
animator_->is_animating(); } and using that instead (here, and also in
Layer::Remove()).

+    LayerAnimatorCollection* collection = GetLayerAnimatorCollection();
+    if (collection)
+      collection->StartAnimator(child->GetAnimator());
+  }
 }
 
 void Layer::Remove(Layer* child) {
@@ -167,6 +172,11 @@ void Layer::Remove(Layer* child) {
   if (child->GetAnimator()) {
     child->GetAnimator()->StopAnimatingProperty(
         ui::LayerAnimationElement::BOUNDS);
+    if (child->GetAnimator()->is_animating()) {
+      LayerAnimatorCollection* collection = GetLayerAnimatorCollection();
+      if (collection)
+        collection->StopAnimator(child->GetAnimator());
+    }
   }
   std::vector<Layer*>::iterator i =
       std::find(children_.begin(), children_.end(), child);
@@ -874,6 +884,11 @@ void Layer::RemoveThreadedAnimation(int animation_id) {
       pending_threaded_animations_.end());
 }
 
+LayerAnimatorCollection* Layer::GetLayerAnimatorCollection() {
+  Compositor* compositor = GetCompositor();
+  return compositor ? compositor->layer_animator_collection() : NULL;
+}
+
 void Layer::SendPendingThreadedAnimations() {
   for (cc::ScopedPtrVector<cc::Animation>::iterator it =
            pending_threaded_animations_.begin();