Remove concept of child Widgets.

sky/engine/platform/FrameWidget.h

Index: sky/engine/platform/FrameWidget.h
diff --git a/sky/engine/platform/FrameWidget.h b/sky/engine/platform/FrameWidget.h
deleted file mode 100644
index d01b0b0d49484e66b8bfd01993052f4f07bcebe1..0000000000000000000000000000000000000000
--- a/sky/engine/platform/FrameWidget.h
+++ /dev/null
@@ -1,23 +0,0 @@
-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef FrameWidget_h
-#define FrameWidget_h
-
-#include "platform/Widget.h"
-
-namespace blink {
-
-class Widget;
-
-class FrameWidget : public Widget {
-public:
-    virtual void removeChild(Widget*) = 0;
-}; // class FrameWidget
-
-DEFINE_TYPE_CASTS(FrameWidget, Widget, widget, widget->isFrameView(), widget.isFrameView());
-
-} // namespace blink
-
-#endif // FrameWidget_h