Decouple GamepadSharedMemory into Blink.

third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.h

Index: third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.h
diff --git a/third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.h b/third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.h
index 6c0d4a0a52ca9dc1dd7005cd7e12fdaec92f88bb..1345768fa64798c7a4640668a186767a04f39e96 100644
--- a/third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.h
+++ b/third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.h
@@ -12,6 +12,7 @@
 
 namespace blink {
 
+class GamepadSharedMemoryReader;
 class WebGamepads;
 
 class GamepadDispatcher final
@@ -54,6 +55,7 @@ class GamepadDispatcher final
                                              bool connected);
 
   ConnectionChange m_latestChange;
+  std::unique_ptr<GamepadSharedMemoryReader> m_reader;
 };
 
 }  // namespace blink