Add service unittest for WakeLockServiceImpl.

device/wake_lock/fake_wake_lock_service_impl.h

+// Copyright 2015 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 DEVICE_WAKE_LOCK_FAKE_WAKE_LOCK_SERVICE_IMPL_H_
+#define DEVICE_WAKE_LOCK_FAKE_WAKE_LOCK_SERVICE_IMPL_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
+#include "device/wake_lock/public/interfaces/wake_lock_context.mojom.h"
+#include "device/wake_lock/public/interfaces/wake_lock_service.mojom.h"
+#include "device/wake_lock/wake_lock_service_impl.h"
+#include "mojo/public/cpp/bindings/binding_set.h"
+#include "ui/gfx/native_widget_types.h"
+
+namespace device {
+
+class FakeWakeLockServiceImpl : public WakeLockServiceImpl {

[blundell, 2017/05/29 13:17:08]

nit: I'd prefer having WakeLockServiceImpl create the PowerSaveBlocker by a
factory function, and then having the test just define a do-nothing
PowerSaveBlocker and inject construction of that as the factory function.

[ke.he, 2017/05/31 11:38:15]

Colin, Sorry I'm not sure If I understanding you correctly or not. 
Do you mean
1) we don't need the FakeWakeLockServiceImpl. And,
2) Add a WakeLockServiceImpl::SetPowerSaveBlockerFactory(), then in production
code we set the factory as WakeLockServiceImpl::CreateWakeLock() while in
testing code set it as CreateDoNothingWakeLock(), right?  In testing code, the
SetPowerSaveBlockerFactory() is still called in WakeLockProvider, after the
WakeLockServiceImpl instance is created, right?  

The type of WakeLockServiceImpl::wake_lock_ is
"std::unique_ptr<PowerSaveBlocker>", so wake_lock_ points to either a real
PowerSaveBlocker instance or nullptr. Then the question is: in the
CreateDoNothingWakeLock(), how can we operate on wake_lock_ to simulate the
PowerSaveBlocker? That's why finally I choose a simpler way, just to create the
FakeWakeLockServiceImpl in which I add a new flag "has_fake_wake_lock_".

Please help give some comments, thanks very much!

+ public:
+  FakeWakeLockServiceImpl(
+      mojom::WakeLockServiceRequest request,
+      mojom::WakeLockType type,
+      mojom::WakeLockReason reason,
+      const std::string& description,
+      int context_id,
+      WakeLockContextCallback native_view_getter,
+      scoped_refptr<base::SingleThreadTaskRunner> file_task_runner);
+  ~FakeWakeLockServiceImpl() override;
+
+  void HasWakeLockForTests(
+      const HasWakeLockForTestsCallback& callback) override;
+
+ private:
+  void UpdateWakeLock() override;
+  void CreateWakeLock() override;
+  void RemoveWakeLock() override;
+
+  bool has_fake_wake_lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(FakeWakeLockServiceImpl);
+};
+
+}  // namespace device
+
+#endif  // DEVICE_WAKE_LOCK_FAKE_WAKE_LOCK_SERVICE_IMPL_H_