Add PlatformLocalFrame class.

third_party/WebKit/Source/platform/PlatformLocalFrame.h

+// Copyright 2017 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 PlatformLocalFrame_h
+#define PlatformLocalFrame_h
+
+#include "platform/PlatformExport.h"
+
+namespace blink {
+
+// PlatformLocalFrame is used in PlatformChromeClient as the platform base class
+// for core/frame/LocalFrame.
+class PLATFORM_EXPORT PlatformLocalFrame {
+ public:
+  PlatformLocalFrame() {}
+  virtual ~PlatformLocalFrame() {}
+
+  virtual bool IsLocalFrame() const { return false; }
+};
+
+}  // namespace blink
+
+#endif  // PlatformLocalFrame_h