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..8632387038a3166bc3895590c0604d15eb8488e1 100644
--- a/device/gamepad/public/interfaces/gamepad.mojom
+++ b/device/gamepad/public/interfaces/gamepad.mojom
@@ -49,3 +49,22 @@ 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);
+
+  [Sync]
+  GamepadStopPolling() => ();
+
+  SetObserver(GamepadObserver gamepad_observer);
+};