cc: Turn SharedQuadState into a struct-like class similar to DrawQuads.

cc/quad_sink.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_QUAD_SINK_H_
 #define CC_QUAD_SINK_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/cc_export.h"
 
 namespace cc {
 
 class DrawQuad;
+class SharedQuadState;
 
 struct AppendQuadsData;
-struct SharedQuadState;
 
 class CC_EXPORT QuadSink {
 public:
     virtual ~QuadSink() { }
 
     // Call this to add a SharedQuadState before appending quads that refer to it. Returns a pointer
     // to the given SharedQuadState for convenience, that can be set on the quads to append.
     virtual SharedQuadState* useSharedQuadState(scoped_ptr<SharedQuadState>) = 0;
 
     // Returns true if the quad is added to the list, and false if the quad is entirely culled.
     virtual bool append(scoped_ptr<DrawQuad> passDrawQuad, AppendQuadsData&) = 0;
 };
 
 }
 #endif  // CC_QUAD_SINK_H_