Expose public interface for composited selection bounds

public/platform/WebLayerTreeView.h

Index: public/platform/WebLayerTreeView.h
diff --git a/public/platform/WebLayerTreeView.h b/public/platform/WebLayerTreeView.h
index 134201641833257cbdaed29ace3b3bf55091f46e..b13138555420eb09dafeea33faf43f0cffc29462 100644
--- a/public/platform/WebLayerTreeView.h
+++ b/public/platform/WebLayerTreeView.h
@@ -42,6 +42,7 @@ class WebLayer;
 struct WebPoint;
 struct WebRect;
 struct WebRenderingStats;
+struct WebSelectionBound;
 
 class WebLayerTreeView {
 public:
@@ -125,6 +126,10 @@ public:
         const WebLayer* outerViewportScrollLayer) { }
     virtual void clearViewportLayers() { }
 
+    // Used to update the active selection bounds.
+    virtual void registerSelection(const WebSelectionBound& anchor, const WebSelectionBound& focus) { }

[abarth-chromium, 2014/06/25 22:27:03]

Are there any invariants of these arguments that we should document?  For
example, is it legal to have one with type Caret and the other with type
SelectionLeft?  Can they both be SelectionRight? 

[jdduke (slow), 2014/06/25 22:58:10]

Yes, good call, I'll flesh out the comment a bit more.  In particular, anchor
and focus will be identical if one is of type Caret (this mirrors the current
|WebView::selectionBounds()| query), and you can indeed have both be of
SelectionRight type with mixed RTL/LTR selections.

+    virtual void clearSelection() { }
+
     // Debugging / dangerous ---------------------------------------------
 
     // Toggles the FPS counter in the HUD layer