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

Source/modules/serviceworkers/ServiceWorkerClients.cpp

 // 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.
 
 #include "config.h"
 #include "modules/serviceworkers/ServiceWorkerClients.h"
 
 #include "bindings/core/v8/CallbackPromiseAdapter.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/dom/ExceptionCode.h"
@@ skipping 55 matching lines @@
     if (options.type() != "window") {
         // FIXME: Currently we only support WindowClients.
         resolver->reject(DOMException::create(NotSupportedError, "type parameter of getAll is not supported."));
         return promise;
     }
 
     ServiceWorkerGlobalScopeClient::from(scriptState->executionContext())->getClients(new CallbackPromiseAdapter<ClientArray, ServiceWorkerError>(resolver));
     return promise;
 }
 
+ScriptPromise ServiceWorkerClients::claim(ScriptState* scriptState)
+{
+    ExecutionContext* executionContext = scriptState->executionContext();
+
+    // FIXME: short-term fix, see details at: https://codereview.chromium.org/535193002/.
+    if (!executionContext)
+        return ScriptPromise();

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

There are other places where such a check isn't done like just above in
::getAll(). Are those buggy?

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

Per that CL... yes. Any method called via bindings that runs in a worker that
calls back into v8 (e.g. ScriptPromiseResolver::create) could fail. That CL also
explicitly mentions getAll() but didn't put in a fix for it.

It's a hack, but we probably want this here (and in getAll); it will affect many
other APIs available to Workers, but we may notice it more frequently with SWs
since they're killed off aggressively.

xiang: what prompted you to add it here specifically?

I would suggest keeping the early exit, adding it to getAll() as well, but
changing the comment to:

// FIXME: May be null due to worker termination. http://crbug.com/388017

(I've pinged that bug and pointed at this CL too)

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

http://crbug.com/413518 has more details, I've just duped 380017 to that. This
is a general problem with worker thread termination. All these checks are just
band-aids to stop from crashing too frequently.

I'm guessing Xiang added it because he was bit by it in skipWaiting:
https://codereview.chromium.org/823583006/

[xiang, 2015/01/26 06:47:54]

updated the comment.

+
+    RefPtrWillBeRawPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(scriptState);
+    ScriptPromise promise = resolver->promise();
+
+    WebServiceWorkerClientsClaimCallbacks* callbacks = new CallbackPromiseAdapter<void, ServiceWorkerError>(resolver);
+    ServiceWorkerGlobalScopeClient::from(executionContext)->claim(callbacks);
+    return promise;
+}
+
 } // namespace blink