Clip constrained windows to the tabcontents bounds.

ui/gfx/compositor/layer.cc

Index: ui/gfx/compositor/layer.cc
===================================================================
--- ui/gfx/compositor/layer.cc	(revision 126769)
+++ ui/gfx/compositor/layer.cc	(working copy)
@@ -171,6 +171,14 @@
   return bounds_;
 }
 
+void Layer::SetMasksToBounds(bool masks_to_bounds) {
+  web_layer_.setMasksToBounds(masks_to_bounds);
+}
+
+bool Layer::GetMasksToBounds() const {
+  return web_layer_.masksToBounds();
+}
+
 void Layer::SetOpacity(float opacity) {
   GetAnimator()->SetOpacity(opacity);
 }