Move ownership of PowerSaveBlocker from WakeLockServiceContext to WakeLockServiceImpl

device/wake_lock/public/interfaces/wake_lock_service.mojom

 // 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.
 
 module device.mojom;
 
 // WebLockService receives wake lock preferences from its client.
 interface WakeLockService {
+  // Requests that a wake lock be applied on behalf of this client. Has no
+  // effect if the client has previously called this method without
+  // subsequently calling CancelWakeLock().
   RequestWakeLock();
+
+  // Cancels any outstanding wake lock request from this client. If there are

[Ken Rockot(use gerrit already), 2017/05/05 17:55:31]

nit: How about "all outstanding wake lock requests" instead of "any outstanding
wake lock request".

[ke.he, 2017/05/06 03:08:43]

Done.

+  // no more outstanding requests from any clients, the active wake lock (if
+  // there is one) will be turned off.
   CancelWakeLock();
+
+  // Adds a client to this WakeLockService instance. Clients are grouped on a
+  // per-WakeLockService instance basis: that is, a given WakeLockService
+  // instance turns on its wake lock whenever *any* of its clients make a
+  // request to do so and turns off its wake lock only when *all* its clients
+  // that had previously called RequestWakelock() cancel their requests.
+  AddClient(WakeLockService& wake_lock);
+
+  // Test-only method that returns whether a wake lock is currently active.
+  HasWakeLockForTests() => (bool result);
 };