Add GetWakeLockWithoutContext() in WakeLockContextProvider mojo interface.

device/wake_lock/public/interfaces/README.md

 Provides the ability to block the device / display from sleeping.
 
 On Android, the implementation is inherently coupled to the NativeView
 associated with the context of the requestor due to system APIs. To handle
 this coupling, the Wake Lock usage model on Android is as follows:
 
 (1) The embedder passes in a callback at Device Service construction that
 enables the Wake Lock implementation to map (embedder-specific) context IDs to
 NativeViews.
 (2) For a given embedder-specific context, a trusted client
-connects to the WakeLockContextProvider interface and gets a
+connects to the WakeLockProvider interface and gets a
 WakeLockContext instance that is associated with that context.
 (3) That trusted client then forwards requests to bind wake locks from
 untrusted clients that are made within that context, with the Wake Lock
 implementation using the callback from (1) as necessary to obtain the
 NativeView associated with that context.
 
 On other platforms, the usage model is similar but the callback is not
 necessary/employed.

[blundell, 2017/05/12 12:42:18]

Let's add comments here about the usage model outside of a context, including
calling out that that means that the Wake Lock will not be functional on
Android.

[ke.he, 2017/05/12 16:09:38]

Done.