Web Animations: Plumb compositor group id through animation creation and start/finish notifications

public/platform/WebCompositorAnimation.h

 // Copyright 2014 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 WebCompositorAnimation_h
 #define WebCompositorAnimation_h
 
 #define WEB_ANIMATION_SUPPORTS_FILL_MODE 1
 
 namespace blink {
@@ skipping 19 matching lines @@
         FillModeNone = 0,
         FillModeForwards,
         FillModeBackwards,
         FillModeBoth
     };
 
     virtual ~WebCompositorAnimation() { }
 
     // An id is effectively the animation's name, and it is not unique.
     virtual int id() = 0;
+    virtual int group() = 0;
 
     virtual TargetProperty targetProperty() const = 0;
 
     // This is the number of times that the animation will play. If this
     // value is zero the animation will not play. If it is negative, then
     // the animation will loop indefinitely.
     virtual double iterations() const = 0;
     virtual void setIterations(double) = 0;
 
     virtual double startTime() const = 0;
@@ skipping 11 matching lines @@
     virtual FillMode fillMode() const = 0;
     virtual void setFillMode(FillMode)  = 0;
 
     virtual double iterationStart() const = 0;
     virtual void setIterationStart(double) = 0;
 };
 
 } // namespace blink
 
 #endif // WebCompositorAnimation_h