Add service unittest for WakeLockServiceImpl.

device/wake_lock/wake_lock_provider.h

Index: device/wake_lock/wake_lock_provider.h
diff --git a/device/wake_lock/wake_lock_provider.h b/device/wake_lock/wake_lock_provider.h
index 0177c287aeccba17278aa78e04e90fd549844736..b3bc9c0321dc31f8f96e29e98789db4b5bfa3009 100644
--- a/device/wake_lock/wake_lock_provider.h
+++ b/device/wake_lock/wake_lock_provider.h
@@ -38,6 +38,8 @@ class WakeLockProvider : public mojom::WakeLockProvider {
       const std::string& description,
       mojom::WakeLockServiceRequest request) override;
 
+  static bool is_in_service_unittest_;
+
  private:
   scoped_refptr<base::SingleThreadTaskRunner> file_task_runner_;
   WakeLockContextCallback native_view_getter_;