Keep track of ServiceWorkerContext's BrowserContext and expose it.

content/browser/service_worker/service_worker_context_core.h

Index: content/browser/service_worker/service_worker_context_core.h
diff --git a/content/browser/service_worker/service_worker_context_core.h b/content/browser/service_worker/service_worker_context_core.h
index ffd0a26446b3d9b99541a5c4fa75bdc3e7374aa3..b977b05eb3d397dab0765fdaa8c0c1f85efbd50a 100644
--- a/content/browser/service_worker/service_worker_context_core.h
+++ b/content/browser/service_worker/service_worker_context_core.h
@@ -196,6 +196,9 @@ class CONTENT_EXPORT ServiceWorkerContextCore
       int new_host_id,
       scoped_ptr<ServiceWorkerProviderHost> provider_host);
 
+  // This MUST be called in the UI thread.

[michaeln, 2015/01/13 21:27:32]

I think this class can remain very strictly single threaded. The wrapper can
have a getter like this for use on the UI thread, and this class can expose a
wrapper() accessor instead. Callers on the IO thread can safely PostTask a
reference to the wrapper over to the UI thread.

[mlamouri (slow - plz ping), 2015/01/14 15:46:24]

Ok. Sounds good. I was assuming SWContextCore wasn't exposing the
SWContextWrapper for some reasons but I guess I should have asked ;)

[michaeln, 2015/01/14 19:57:02]

The wrapper() was intentionally not exposed to help avoid the introduction of
odd/uneeded dependencies on stuff with affinity to other threads. The
clients.open function requires exactly that so it makes sense to add it now.

+  BrowserContext* GetBrowserContext() const;
+
   base::WeakPtr<ServiceWorkerContextCore> AsWeakPtr() {
     return weak_factory_.GetWeakPtr();
   }