Allow impl-only animations, and return opacity values via AnimationEvents.

cc/animation_events.h

 // Copyright 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.
 
 #ifndef CC_ANIMATION_EVENTS_H_
 #define CC_ANIMATION_EVENTS_H_
 
 #include <vector>
 
 #include "cc/animation.h"
 
 namespace cc {
 
 struct AnimationEvent {
-    enum Type { Started, Finished };
+    enum Type { Started, Finished, PropertyUpdate };
 
-    AnimationEvent(Type type, int layerId, int groupId, Animation::TargetProperty targetProperty, double monotonicTime)
+    AnimationEvent(Type type, int layerId, int groupId, Animation::TargetProperty targetProperty, double monotonicTime, float val = 0)
         : type(type)
         , layerId(layerId)
         , groupId(groupId)
         , targetProperty(targetProperty)
         , monotonicTime(monotonicTime)
+        , value(val)

[Ian Vollick, 2013/03/06 01:00:57]

nit: Since I'd like to support plumbing back transforms, I would prefer to avoid
the default parameter and have the constructor initialize the float and
transform values to 0 and I, respectively. Anyone sending back property updates
should set the value as a separate step.

[wjmaclean, 2013/03/06 17:03:13]

Done.

     {
     }
 
     Type type;
     int layerId;
     int groupId;
     Animation::TargetProperty targetProperty;
     double monotonicTime;
+    float value;

[Ian Vollick, 2013/03/06 01:00:57]

I know that you're only interested in floats at the moment, but if we're going
to allow property updates to bubble back, I'd prefer to allow for transforms as
well.

[wjmaclean, 2013/03/06 17:03:13]

Done.

 };
 
 typedef std::vector<AnimationEvent> AnimationEventsVector;
 
 }  // namespace cc
 
 #endif  // CC_ANIMATION_EVENTS_H_