Convert Gamepad IPC messages into mojo interface.

device/gamepad/public/interfaces/gamepad.mojom

Index: device/gamepad/public/interfaces/gamepad.mojom
diff --git a/device/gamepad/public/interfaces/gamepad.mojom b/device/gamepad/public/interfaces/gamepad.mojom
index 5fbd79f824f7edeb38b6a30801bdaad273c8f7e7..6864192796a4fcf9249bc6a2218745d825b4d753 100644
--- a/device/gamepad/public/interfaces/gamepad.mojom
+++ b/device/gamepad/public/interfaces/gamepad.mojom
@@ -49,3 +49,19 @@ struct Gamepad {
   GamepadHand hand;
   uint32 display_id;
 };
+
+interface GamepadObserver {
+  GamepadConnected(int32 index, Gamepad gamepad);
+  GamepadDisconnected(int32 index, Gamepad gamepad);
+};
+
+// Asks the browser process to start polling, and return a shared memory
+// handles that will hold the data from the hardware. See
+// gamepad_hardware_buffer.h for a description of how synchronization is
+// handled. The number of Starts should match the number of Stops.
+interface GamepadMonitor {
+  [Sync]
+  GamepadStartPolling() => (handle<shared_buffer> memory_handle);
+  GamepadStopPolling();

[blundell, 2016/12/01 16:01:26]

Did you reason about whether this one should be sync as well (as it was in the
old impl)?

[ke.he, 2016/12/02 13:20:47]

It should be Sync as it was in the old impl. Thanks!
done.

+  SetObserver(GamepadObserver gamepad_observer);
+};