Break out EventDispatchingWindow into separate class

brightray/browser/mac/event_dispatching_window.h

@@ -0,0 +1,19 @@
+// Copyright (c) 2016 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef BROWSER_EVENT_DISPATCHING_WINDOW_H_
+#define BROWSER_EVENT_DISPATCHING_WINDOW_H_
+
+#import "ui/base/cocoa/underlay_opengl_hosting_window.h"
+
+@interface EventDispatchingWindow : UnderlayOpenGLHostingWindow {
+ @private
+  BOOL redispatchingEvent_;
+}
+
+- (void)redispatchKeyEvent:(NSEvent*)event;
+
+@end
+
+#endif  // BROWSER_EVENT_DISPATCHING_WINDOW_H_