Make Screen Orientation use Platform Events in order to handle polling.

Source/modules/screen_orientation/ScreenOrientationDispatcher.h

+// 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 ScreenOrientationDispatcher_h
+#define ScreenOrientationDispatcher_h
+
+#include "core/frame/PlatformEventDispatcher.h"
+
+namespace blink {
+
+class FrameView;
+class ScreenOrientation;
+
+// ScreenOrientationDispatcher is a singleton that handles whether the current
+// Blink instance should be listening to the screen orientation platform events.
+// It is not a common implementation of PlatformEventDispatcher in the sense
+// that it doesn't actually dispatch events but simply start/stop listening. The
+// reason being that screen orientation events are always sent to the WebFrame's
+// but some platforms require to poll to have an accurate reporting. When
+// ScreenOrientationDispatcher is listening, that means that the platform should
+// be polling if required.
+class ScreenOrientationDispatcher FINAL :
+    public PlatformEventDispatcher {
+public:
+    static ScreenOrientationDispatcher& instance();
+
+private:
+    ScreenOrientationDispatcher();
+    virtual ~ScreenOrientationDispatcher();
+
+    // Inherited from PlatformEventDispatcher.
+    virtual void startListening() OVERRIDE;
+    virtual void stopListening() OVERRIDE;
+};
+
+} // namespace blink
+
+#endif // ScreenOrientationDispatcher_h