Move ownership of PowerSaveBlocker from WakeLockServiceContext to WakeLockServiceImpl

device/wake_lock/public/interfaces/wake_lock_service.mojom

Index: device/wake_lock/public/interfaces/wake_lock_service.mojom
diff --git a/device/wake_lock/public/interfaces/wake_lock_service.mojom b/device/wake_lock/public/interfaces/wake_lock_service.mojom
index 8c6e7a494c0f32fd97537713ab2222585860d65f..534fcf860a77b74d8144010c43c2f52b0cf45f98 100644
--- a/device/wake_lock/public/interfaces/wake_lock_service.mojom
+++ b/device/wake_lock/public/interfaces/wake_lock_service.mojom
@@ -6,6 +6,19 @@ module device.mojom;
 
 // WebLockService receives wake lock preferences from its client.
 interface WakeLockService {
+  // Request WakeLock Service from WakeLockServiceImpl.

[blundell, 2017/05/05 12:49:37]

nit: I would write something like:

"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
RequestWakeLock()."

[ke.he, 2017/05/05 14:56:36]

Thanks very much. I'm sorry for my poor english.
"subsequently calling RequestWakeLock()" -> "subsequently calling
CancelWakeLock()", right?

+  // Each WakeLockServiceImpl instance owns only 1 PowerSaveBlocker. 
+  // If client calls RequestWakeLock() multiple times consecutively,
+  // WakeLockServiceImpl only handles the first one.
   RequestWakeLock();
+
+  // Cancel WakeLock Service.

[blundell, 2017/05/05 12:49:37]

"Cancels any outstanding wake lock request from this client. If there are no
more outstanding requests from any clients, the active wake lock (if there is
one) will be turned off)."

[ke.he, 2017/05/05 14:56:36]

Done.

   CancelWakeLock();
+
+  // Add other clients to current WakeLockServiceImpl so it can serve multiple

[blundell, 2017/05/05 12:49:37]

"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."

[ke.he, 2017/05/05 14:56:36]

Done.

+  // clients.
+  AddClient(WakeLockService& wake_lock);
+
+  // Test-only method that returns whether a wake lock is currently active.
+  HasWakeLockForTests() => (bool result);
 };