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

cc/animation.h

Index: cc/animation.h
diff --git a/cc/animation.h b/cc/animation.h
index 37b6e31131de0f3f30f07d1debf151d51581ffc4..94cb8f243d9fcdc9fb232aa0e650343a412a8965 100644
--- a/cc/animation.h
+++ b/cc/animation.h
@@ -107,6 +107,9 @@ public:
 
     void pushPropertiesTo(Animation*) const;
 
+    void setIsImplOnly(bool isImplOnly) { m_isImplOnly = isImplOnly; }
+    bool isImplOnly() { return  m_isImplOnly; }
+
 private:
     Animation(scoped_ptr<AnimationCurve>, int animationId, int groupId, TargetProperty);
 
@@ -155,6 +158,8 @@ private:
     // to it as the 'controlling instance'.
     bool m_isControllingInstance;
 
+    bool m_isImplOnly;
+
     DISALLOW_COPY_AND_ASSIGN(Animation);
 };