Refactor code listening to platform events in content/renderer/.

This is introducing PlatformEventObserver, being used by code observing
and requesting platform events like Gamepad, Device Motion, Device
Orientation, Device Light and Battery.

BUG=400158

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=288555

Review URL: https://codereview.chromium.org/446603002

Cr-Commit-Position: refs/heads/master@{#290563}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@290563 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/content/renderer/gamepad_shared_memory_reader.h b/content/renderer/gamepad_shared_memory_reader.h
index eb63867..d62f881 100644
--- a/content/renderer/gamepad_shared_memory_reader.h
+++ b/content/renderer/gamepad_shared_memory_reader.h
@@ -8,46 +8,40 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/shared_memory.h"
 #include "content/common/gamepad_messages.h"
-#include "content/public/renderer/render_process_observer.h"
 #include "content/public/renderer/renderer_gamepad_provider.h"
 #include "third_party/WebKit/public/platform/WebGamepads.h"
 
 namespace content {
 
 struct GamepadHardwareBuffer;
-class RendererWebKitPlatformSupportImpl;
 
-class GamepadSharedMemoryReader
-    : public RenderProcessObserver,
-      public RendererGamepadProvider {
+class GamepadSharedMemoryReader : public RendererGamepadProvider {
  public:
-  GamepadSharedMemoryReader(
-      RendererWebKitPlatformSupportImpl* webkit_platform_support);
+  explicit GamepadSharedMemoryReader(RenderThread* thread);
   virtual ~GamepadSharedMemoryReader();
 
   // RendererGamepadProvider implementation.
   virtual void SampleGamepads(
       blink::WebGamepads& gamepads) OVERRIDE;
-  virtual void SetGamepadListener(
-      blink::WebGamepadListener* listener) OVERRIDE;
-
-  // RenderProcessObserver implementation.
   virtual bool OnControlMessageReceived(const IPC::Message& message) OVERRIDE;
+  virtual void Start(blink::WebPlatformEventListener* listener) OVERRIDE;
+
+ protected:
+  // PlatformEventObserver protected methods.
+  virtual void SendStartMessage() OVERRIDE;
+  virtual void SendStopMessage() OVERRIDE;
 
  private:
   void OnGamepadConnected(int index, const blink::WebGamepad& gamepad);
   void OnGamepadDisconnected(int index, const blink::WebGamepad& gamepad);
 
-  void StartPollingIfNecessary();
-  void StopPollingIfNecessary();
-
   base::SharedMemoryHandle renderer_shared_memory_handle_;
   scoped_ptr<base::SharedMemory> renderer_shared_memory_;
   GamepadHardwareBuffer* gamepad_hardware_buffer_;
-  blink::WebGamepadListener* gamepad_listener_;
 
-  bool is_polling_;
   bool ever_interacted_with_;
+
+  DISALLOW_COPY_AND_ASSIGN(GamepadSharedMemoryReader);
 };
 
 }  // namespace content