MacViews: Clip contents for non-rectangular windows.

ui/views/cocoa/bridged_native_widget.h

Index: ui/views/cocoa/bridged_native_widget.h
diff --git a/ui/views/cocoa/bridged_native_widget.h b/ui/views/cocoa/bridged_native_widget.h
index 8f6523042de9eead7500964bd6d0daee8883ae63..fb50a3c8da492b248c2351c7d10e36e65ea5b790 100644
--- a/ui/views/cocoa/bridged_native_widget.h
+++ b/ui/views/cocoa/bridged_native_widget.h
@@ -31,6 +31,7 @@ class InputMethod;
 namespace views {
 namespace test {
 class BridgedNativeWidgetTestApi;
+class BridgedNativeWidgetTest;
 }
 
 class CocoaMouseCapture;
@@ -178,6 +179,7 @@ class VIEWS_EXPORT BridgedNativeWidget
 
  private:
   friend class test::BridgedNativeWidgetTestApi;
+  friend class test::BridgedNativeWidgetTest;
 
   // Closes all child windows. BridgedNativeWidget children will be destroyed.
   void RemoveOrDestroyChildren();
@@ -215,6 +217,11 @@ class VIEWS_EXPORT BridgedNativeWidget
   // update its draggable region.
   void SetDraggable(bool draggable);
 
+  // Calls updateWindowMask on |bridged_view_| and updates the mask path for
+  // |compositor_superview_|'s layer. If a mask layer does not yet exist, it
+  // creates a new one.
+  void UpdateMaskPath();
+
   // Overridden from CocoaMouseCaptureDelegate:
   void PostCapturedEvent(NSEvent* event) override;
   void OnMouseCaptureLost() override;