Service Worker: Correct WindowClient.idl

Source/modules/serviceworkers/WindowClient.idl

 // Copyright 2014 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.
 
 // https://slightlyoff.github.io/ServiceWorker/spec/service_worker/#context-frame-type-enum
 enum ContextFrameType {
     "top-level",
     "nested",
     "auxiliary",
     "none"
 };
 
 // https://slightlyoff.github.io/ServiceWorker/spec/service_worker/#window-client-interface
 [
     Exposed=ServiceWorker,
     RuntimeEnabled=ServiceWorkerClientAttributes,
     GarbageCollected,
     TypeChecking=Interface,
     ImplementedAs=ServiceWorkerWindowClient,
 ] interface WindowClient : Client {
     readonly attribute VisibilityState visibilityState;
     readonly attribute boolean focused;
-    readonly attribute ContextFrameType frameType;

[zino, 2015/07/03 02:38:57]

Clarify: This is already defined in Client and we don't need to redefine.
            This change doesn't affect any behavior.

-    [CallWith=ScriptState] Promise<boolean> focus();
+    [CallWith=ScriptState] Promise<WindowClient> focus();

[nhiroki, 2015/07/03 03:18:08]

A promise resolution value type is just an annotation in WebIDL, so this change
does not affect actual implementation. OK, LGTM.

[falken, 2015/07/03 03:22:49]

Doesn't the C++ code need updating too? I assume we're resolving with a boolean
now.

And we don't have tests that test the return value of focus()? Can you add them?

 };