exo: Implement wayland gamepad support

components/exo/gamepad.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_EXO_GAMEPAD_H_
+#define COMPONENTS_EXO_GAMEPAD_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sequenced_task_runner.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "device/gamepad/gamepad_data_fetcher.h"
+#include "ui/aura/client/focus_change_observer.h"
+
+namespace exo {
+class GamepadDelegate;
+
+typedef base::Callback<std::unique_ptr<device::GamepadDataFetcher>()>

[reveman, 2016/07/11 10:50:44]

nit: using CreateGamepadDataFetcherCallback = base::Callback<...

"using" is preferred and when it's just a single callback I prefer the
"Create*Callback" name instead of *Factory

[denniskempin, 2016/07/11 17:43:28]

Done.

+    GamepadDataFetcherFactory;
+
+// This class represents one or more gamepads, it implements a background thread
+// for polling gamepad devices and notifies the GamepadDelegate of any
+// changes.
+class Gamepad : public aura::client::FocusChangeObserver {
+ public:
+  // This class will post tasks to invoke the delegate on the thread runner
+  // which is associated with the thread that is creating this instance.
+  Gamepad(GamepadDelegate* delegate,
+          scoped_refptr<base::SingleThreadTaskRunner> polling_task_runner);

[reveman, 2016/07/11 10:50:44]

nit: this will result in unnecessary ref-count churn. please use
"base::SingleThreadTaskRunner* polling_task_runner" instead.

[denniskempin, 2016/07/11 17:43:28]

Done.

+  // Allows test cases to specify a GamepadDataFetcherFactory that overrides
+  // the default PlatformGamepadDataFetcher.
+  Gamepad(GamepadDelegate* delegate,
+          scoped_refptr<base::SingleThreadTaskRunner> polling_task_runner,

[reveman, 2016/07/11 10:50:44]

nit: "base::SingleThreadTaskRunner* polling_task_runner" instead

[denniskempin, 2016/07/11 17:43:28]

Done.

+          GamepadDataFetcherFactory fetcher_factory);
+  ~Gamepad() override;
+
+  // Overridden aura::client::FocusChangeObserver:
+  void OnWindowFocused(aura::Window* gained_focus,
+                       aura::Window* lost_focus) override;
+
+ private:
+  // Private implementation of methods and resources that are used on the
+  // polling thread.
+  class PollingThreadResources;
+  scoped_refptr<PollingThreadResources> polling_thread_resources_;

[reveman, 2016/07/11 10:50:44]

nit: member variables below types and functions

[denniskempin, 2016/07/11 17:43:28]

Done.

+
+  // Posts updates of gamepad data to delegate. Can only be called on the
+  // origin thread.
+  void PostGamepadChanges(const blink::WebGamepad new_pad);

[reveman, 2016/07/11 10:50:44]

nit: "Handle" or "Process" instead of "Post" as post is typically used for
asynchronous processing of tasks and that's not the case here. Please update
comment too.

[denniskempin, 2016/07/11 17:43:28]

Done.

+
+  // Method implementing the default GamepadDataFetcherFactory, returning
+  // ownership of an instance of GamepadPlatformDataFetcher.
+  static std::unique_ptr<device::GamepadDataFetcher>
+  GamepadPlatformDataFetcherFactory();

[reveman, 2016/07/11 10:50:44]

nit: either move this into anonymouse namespace in .cc file or remove the ctor
that doesn't take a create fetcher callback 

[denniskempin, 2016/07/11 17:43:28]

Done.

+
+  // The delegate instance that all events are dispatched to.
+  GamepadDelegate* const delegate_;
+
+  // The current state of the gamepad represented by this instance.
+  blink::WebGamepad pad_state_;
+
+  // ThreadChecker for the origin thread.
+  base::ThreadChecker thread_checker_;
+
+  base::WeakPtrFactory<Gamepad> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(Gamepad);
+};
+
+}  // namespace exo
+
+#endif  // COMPONENTS_EXO_GAMEPAD_H_