Move ownership of PowerSaveBlocker from WakeLockServiceContext to WakeLockServiceImpl

device/wake_lock/public/interfaces/wake_lock_context.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;
 
 import "device/wake_lock/public/interfaces/wake_lock_service.mojom";
 
 // Context in which WakeLockService instances operate.
 interface WakeLockContext {
   // Gets a WakeLockService within this context.
   GetWakeLock(WakeLockService& wake_lock);
-
-  // Test-only method that returns whethere a wake lock is currently active
-  // within this context.
-  HasWakeLockForTests() => (bool result);
 };