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

Source/modules/serviceworkers/ServiceWorkerClients.cpp

Index: Source/modules/serviceworkers/ServiceWorkerClients.cpp
diff --git a/Source/modules/serviceworkers/ServiceWorkerClients.cpp b/Source/modules/serviceworkers/ServiceWorkerClients.cpp
index 6e5ed30b07f19a82d15b58b073abde469a56bf41..0f1c68ceabcc080842497346ed2560054e95d2df 100644
--- a/Source/modules/serviceworkers/ServiceWorkerClients.cpp
+++ b/Source/modules/serviceworkers/ServiceWorkerClients.cpp
@@ -73,4 +73,20 @@ ScriptPromise ServiceWorkerClients::getAll(ScriptState* scriptState, const Clien
     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