Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

cc/pinch_zoom_scrollbar_layer.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_PINCH_ZOOM_SCROLLBAR_LAYER_H_
+#define CC_PINCH_ZOOM_SCROLLBAR_LAYER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "cc/layer.h"
+
+namespace cc {
+
+class PinchZoomScrollbarLayer : public Layer {

[enne (OOO), 2012/12/13 17:43:38]

I'm really not seeing what this is for.  Can you just store the id of the layer
you want to attach the layer impls to rather than creating layers in the tree? 
That would eliminate these classes and 90% of the code that you've added in LTH.

[wjmaclean, 2012/12/13 18:26:50]

How do I get a valid layer ID to use when creating my SLI's?

+public:
+    static scoped_refptr<PinchZoomScrollbarLayer> create();
+
+    virtual scoped_ptr<LayerImpl> createLayerImpl(LayerTreeImpl* treeImpl) OVERRIDE;
+    virtual bool drawsContent() const OVERRIDE;
+
+private:
+    explicit PinchZoomScrollbarLayer();
+    virtual ~PinchZoomScrollbarLayer() { }
+
+}; // class PinchZoomScrollbarLayer
+
+} // namespace cc
+#endif // CC_PINCH_ZOOM_SCROLLBAR_LAYER_H_