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

cc/layer_tree_host.h

Index: cc/layer_tree_host.h
diff --git a/cc/layer_tree_host.h b/cc/layer_tree_host.h
index 3407dba4b20ffbe5d362ca44fece2e5ec2b6652c..4e834ec6843e5dec6934e275b04e2a51a520c992 100644
--- a/cc/layer_tree_host.h
+++ b/cc/layer_tree_host.h
@@ -53,6 +53,7 @@ class PrioritizedResource;
 class Region;
 class ResourceProvider;
 class ResourceUpdateQueue;
+class ScrollbarLayer;
 class TopControlsManager;
 struct ScrollAndScaleSet;
 
@@ -97,6 +98,8 @@ public:
     void layout();
     void beginCommitOnImplThread(LayerTreeHostImpl*);
     void finishCommitOnImplThread(LayerTreeHostImpl*);
+    void setPinchZoomScrollbarsBoundsAndPosition();
+    void createAndAddPinchZoomScrollbars();
     void willCommit();
     void commitComplete();
     scoped_ptr<OutputSurface> createOutputSurface();
@@ -152,6 +155,8 @@ public:
     void setAnimationEvents(scoped_ptr<AnimationEventsVector>, base::Time wallClockTime);
 
     Layer* rootLayer() { return m_rootLayer.get(); }
+    Layer* rootScrollLayer() const;

[jamesr, 2013/03/02 03:19:14]

Do you still need this?

[wjmaclean, 2013/03/04 15:53:10]

Yes, I believe so. In order for a PZ scrollbar to paint, its ScrollbarLayer
calls the PinchZoomScrollbar object as part of determining the thumb geometry,
and since this information isn't coming from WebKit, the PinchZoomScrollbar
needs to be able to pull it from the root scroll layer.

This function allows a caller external to LTH to get access to
findFirstScrollableLayer(), though I suppose we could expose that instead, or
possible have PinchZoomScrollbar replicate LTH's logic for doing this (though I
suspect that would be harder to maintain).

+
     const Layer* rootLayer() const { return m_rootLayer.get(); }
     void setRootLayer(scoped_refptr<Layer>);
 
@@ -253,6 +258,8 @@ private:
 
     scoped_refptr<Layer> m_rootLayer;
     scoped_refptr<HeadsUpDisplayLayer> m_hudLayer;
+    scoped_refptr<ScrollbarLayer> m_pinchZoomScrollbarHorizontal;
+    scoped_refptr<ScrollbarLayer> m_pinchZoomScrollbarVertical;
 
     scoped_ptr<PrioritizedResourceManager> m_contentsTextureManager;
     scoped_ptr<PrioritizedResource> m_surfaceMemoryPlaceholder;