MacViews: Add WidgetEventGenerator to abstract platform-specific event generation for tests.

ui/views/widget/native_widget_mac.h

Index: ui/views/widget/native_widget_mac.h
diff --git a/ui/views/widget/native_widget_mac.h b/ui/views/widget/native_widget_mac.h
index 0cd87b719ee2a7ad247a6d5603d0966c6bed0a79..8996a71960c2264307e940df2786a73184fd17b7 100644
--- a/ui/views/widget/native_widget_mac.h
+++ b/ui/views/widget/native_widget_mac.h
@@ -104,6 +104,9 @@ class VIEWS_EXPORT NativeWidgetMac : public internal::NativeWidgetPrivate {
   virtual void OnRootViewLayout() const OVERRIDE;
   virtual void RepostNativeEvent(gfx::NativeEvent native_event) OVERRIDE;
 
+ protected:
+  internal::NativeWidgetDelegate* delegate() { return delegate_; }
+
  private:
   internal::NativeWidgetDelegate* delegate_;
   scoped_ptr<BridgedNativeWidget> bridge_;