Modify the RenderThread to track the number of widgets...

chrome/renderer/render_widget.h

Index: chrome/renderer/render_widget.h
===================================================================
--- chrome/renderer/render_widget.h	(revision 24223)
+++ chrome/renderer/render_widget.h	(working copy)
@@ -151,6 +151,11 @@
   // browser side has updated the screen for a newly painted region.
   virtual void DidPaint() {}
 
+  // Sets the "hidden" state of this widget.  All accesses to is_hidden_ should
+  // use this method so that we can properly inform the RenderThread of our
+  // state.
+  void SetHidden(bool hidden);
+
   // True if a PaintRect_ACK message is pending.
   bool paint_reply_pending() const {
     return paint_reply_pending_;