Decouple GamepadSharedMemory into Blink.

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

Index: third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.cpp
diff --git a/third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.cpp b/third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.cpp
index 21dd5af0cc058afa6701c940b1782a03324b3405..0ff0436e0e2415443a5a62a427192fd89647128b 100644
--- a/third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.cpp
+++ b/third_party/WebKit/Source/modules/gamepad/GamepadDispatcher.cpp
@@ -4,6 +4,7 @@
 
 #include "modules/gamepad/GamepadDispatcher.h"
 
+#include "modules/gamepad/GamepadSharedMemoryReader.h"
 #include "modules/gamepad/NavigatorGamepad.h"
 #include "public/platform/Platform.h"
 
@@ -50,11 +51,17 @@ void GamepadDispatcher::dispatchDidConnectOrDisconnectGamepad(
 }
 
 void GamepadDispatcher::startListening() {
-  Platform::current()->startListening(WebPlatformEventTypeGamepad, this);
+  if (!m_reader.get()) {
+    m_reader.reset(new GamepadSharedMemoryReader(
+        Platform::current()->interfaceProvider()));
+  }
+  m_reader->start(this);
 }
 
 void GamepadDispatcher::stopListening() {
-  Platform::current()->stopListening(WebPlatformEventTypeGamepad);
+  if (m_reader) {
+    m_reader->stop();
+  }
 }
 
 }  // namespace blink