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

ui/compositor/layer_animation_sequence.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/compositor/layer_animation_sequence.h"
 
 #include <algorithm>
 #include <iterator>
 
 #include "base/trace_event/trace_event.h"
@@ skipping 30 matching lines @@
   for (auto& observer : observers_)
     observer.DetachedFromSequence(this, true);
 }
 
 void LayerAnimationSequence::Start(LayerAnimationDelegate* delegate) {
   DCHECK(start_time_ != base::TimeTicks());
   last_progressed_fraction_ = 0.0;
   if (elements_.empty())
     return;
 
+  elements_[0]->set_requested_start_time(start_time_);
+  elements_[0]->Start(delegate, animation_group_id_);
+
   NotifyStarted();
 
-  elements_[0]->set_requested_start_time(start_time_);
-  elements_[0]->Start(delegate, animation_group_id_);
+  // This may have been aborted.
 }
 
 void LayerAnimationSequence::Progress(base::TimeTicks now,
                                       LayerAnimationDelegate* delegate) {
   DCHECK(start_time_ != base::TimeTicks());
   bool redraw_required = false;
 
   if (elements_.empty())
     return;
 
@@ skipping 209 matching lines @@
 
 LayerAnimationElement* LayerAnimationSequence::CurrentElement() const {
   if (elements_.empty())
     return NULL;
 
   size_t current_index = last_element_ % elements_.size();
   return elements_[current_index].get();
 }
 
 }  // namespace ui