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

cc/layer.h

 // Copyright 2010 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_LAYER_H_
 #define CC_LAYER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 36 matching lines @@
 
 // Base class for composited layers. Special layer types are derived from
 // this class.
 class CC_EXPORT Layer : public base::RefCounted<Layer>,
                         public LayerAnimationValueObserver {
 public:
     typedef std::vector<scoped_refptr<Layer> > LayerList;
 
     static scoped_refptr<Layer> create();
 
+    static const int s_invalidLayerId;

[enne (OOO), 2013/03/11 21:08:24]

Can you make this an enum to not require storage for this value?

Also, 0 is the invalid layer id.  -1 here means something special for pinch zoom
scrollbars in that they are managed by LayerTreeImpl specially.  Can you make
them different values?

[wjmaclean, 2013/03/12 16:13:07]

Yes, good idea!
Hmm, if you refer back to comment #20, James R requested that I *don't* use 0,
on the grounds that -1 is the invalid layer id (not the exact same context, but
still we're marking invalid layers). I can live with either, but it would be
good if there could be a common consensus on which value to use.

I have proposed the following solution in the revised patch:

-1 => invalid layer
0 => unused layer (PZ scrollbar layers use this for scrolling layer id)

     int id() const;
 
     Layer* rootLayer();
     Layer* parent() { return m_parent; }
     const Layer* parent() const { return m_parent; }
     void addChild(scoped_refptr<Layer>);
     void insertChild(scoped_refptr<Layer>, size_t index);
     void replaceChild(Layer* reference, scoped_refptr<Layer> newLayer);
     void removeFromParent();
     void removeAllChildren();
@@ skipping 337 matching lines @@
     WebKit::WebLayerScrollClient* m_layerScrollClient;
 
     DrawProperties<Layer, RenderSurface> m_drawProperties;
 };
 
 void sortLayers(std::vector<scoped_refptr<Layer> >::iterator, std::vector<scoped_refptr<Layer> >::iterator, void*);
 
 }  // namespace cc
 
 #endif  // CC_LAYER_H_