[Mac] Rubber-banding on Lion.

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
===================================================================
--- content/renderer/render_widget.cc	(revision 96200)
+++ content/renderer/render_widget.cc	(working copy)
@@ -831,6 +831,7 @@
   params.plugin_window_moves.swap(plugin_window_moves_);
   params.flags = next_paint_flags_;
   params.scroll_offset = GetScrollOffset();
+  params.contents_size = GetContentsSize();
 
   update_reply_pending_ = true;
   Send(new ViewHostMsg_UpdateRect(routing_id_, params));
@@ -1248,6 +1249,11 @@
   return gfx::Point(0, 0);
 }
 
+gfx::Size RenderWidget::GetContentsSize() {
+  // Bare RenderWidgets don't support contents size.
+  return gfx::Size(0, 0);
+}
+
 void RenderWidget::SetHidden(bool hidden) {
   if (is_hidden_ == hidden)
     return;