[ash-md] Enhanced LayerAnimator to allow animations to be aborted/started in OnLayerAnimationStarte…

ui/compositor/layer_animation_sequence.cc

Index: ui/compositor/layer_animation_sequence.cc
diff --git a/ui/compositor/layer_animation_sequence.cc b/ui/compositor/layer_animation_sequence.cc
index 50b08e2ae6b597f6ba09ffd77d7da8dd46828c89..8d776fd454847d8317820516d066c6d4d13b1745 100644
--- a/ui/compositor/layer_animation_sequence.cc
+++ b/ui/compositor/layer_animation_sequence.cc
@@ -48,10 +48,12 @@ void LayerAnimationSequence::Start(LayerAnimationDelegate* delegate) {
   if (elements_.empty())
     return;
 
-  NotifyStarted();
-
   elements_[0]->set_requested_start_time(start_time_);
   elements_[0]->Start(delegate, animation_group_id_);
+
+  NotifyStarted();
+
+  // This may have been aborted.
 }
 
 void LayerAnimationSequence::Progress(base::TimeTicks now,