ServiceWorker: register() should return the existing registration object if available

public/platform/WebServiceWorkerRegistrationProxy.h

 // 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.
 
 #ifndef WebServiceWorkerRegistrationProxy_h
 #define WebServiceWorkerRegistrationProxy_h
 
+#include "public/platform/WebCommon.h"
+
 namespace blink {
 
+class ServiceWorkerRegistration;
 class WebServiceWorker;
 
 // A proxy interface, passed via WebServiceWorkerRegistration.setProxy() from
 // blink to the embedder, to talk to the ServiceWorkerRegistration object from
 // embedder.
 class WebServiceWorkerRegistrationProxy {
 public:
-    WebServiceWorkerRegistrationProxy() { }
+    WebServiceWorkerRegistrationProxy() : m_private(0) { }
     virtual ~WebServiceWorkerRegistrationProxy() { }
 
     // Notifies that the registration entered the installation process.
     // The installing worker should be accessible via
     // WebServiceWorkerRegistration.installing.
     virtual void dispatchUpdateFoundEvent() = 0;
 
     virtual void setInstalling(WebServiceWorker*) = 0;
     virtual void setWaiting(WebServiceWorker*) = 0;
     virtual void setActive(WebServiceWorker*) = 0;
+
+#if INSIDE_BLINK
+    BLINK_PLATFORM_EXPORT WebServiceWorkerRegistrationProxy(ServiceWorkerRegistration*);
+    BLINK_PLATFORM_EXPORT operator ServiceWorkerRegistration*() const;
+#endif
+
+protected:
+    ServiceWorkerRegistration* m_private;

[sof, 2014/08/14 08:59:49]

This is a GCed object; can you guarantee that the object is otherwise referenced
and kept alive for the duration of this proxy object?

(I guess what I'm really asking is why this isn't wrapped in a WebPrivatePtr<>.)

[nhiroki, 2014/08/15 00:05:54]

Thank you for pointing out! I think our subsequent CLs will ensure that the
proxy is never accessed after it stops, and I'll consider the WebPrivatePtr<>
way (sorry, I don't really understand that pointer yet).


Following lists are just my memo about the lifetime of the proxy object:

1) ServiceWorkerRegistration is not GCed until ServiceWorkerRegistration::stop()
is called (see https://codereview.chromium.org/467133002/).
2) After the registration is stoped, |m_private| is no longer accessed
(CallbackPromiseAdapter doesn't call ServiceWorkerRegistration::take()).
3) When the proxy stops, the embedder is notified via
WebServiceWorkerRegistration::proxyStopped() and stops using the proxy object
(I'm making the chromium-side CL for this).

 };
 
 } // namespace blink
 
 #endif // WebServiceWorkerRegistrationProxy_h