ServiceWorker: add ServiceWorkerClients.claim() support (1/3).

Source/modules/serviceworkers/Clients.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/#clients-interface
 [
     Exposed=ServiceWorker,
     RuntimeEnabled=ServiceWorker,
     GarbageCollected,
     TypeChecking=Interface,
     ImplementedAs=ServiceWorkerClients,
 ] interface Clients {
     [CallWith=ScriptState] Promise<sequence<Client>?> getAll(optional ClientQueryOptions options);
+    [CallWith=ScriptState] Promise claim();

[mlamouri (slow - plz ping), 2015/01/23 10:08:08]

Shouldn't that be being a feature flag?

[jsbell, 2015/01/24 00:42:16]

If it's a non-controversial addition to the core feature set we don't have to go
through the intent/flag process. falken@ should probably make the call (I
haven't been tracking SW spec development as closely)

[falken, 2015/01/26 04:55:11]

We'll go through the "Intent to Implement and Ship" process. As it's a
functionality that has been in the spec since the beginning (though in a
different form as "replace()") I don't really expect controversy but we'll get
that intent out ASAP. If it fails to gain approval we'll revert before the
branch point.

 };