Remove ContextLifecycleObserver from NavigatorServiceWorker

third_party/WebKit/Source/modules/serviceworkers/NavigatorServiceWorker.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 "modules/serviceworkers/NavigatorServiceWorker.h"
 
 #include "core/dom/Document.h"
 #include "core/frame/LocalDOMWindow.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Navigator.h"
 #include "modules/serviceworkers/ServiceWorkerContainer.h"
 
 namespace blink {
 
-NavigatorServiceWorker::NavigatorServiceWorker(Navigator& navigator)
-    : ContextLifecycleObserver(navigator.frame() ? navigator.frame()->document()
-                                                 : nullptr) {}
+NavigatorServiceWorker::NavigatorServiceWorker(Navigator& navigator) {}
 
 NavigatorServiceWorker* NavigatorServiceWorker::from(Document& document) {
   if (!document.frame() || !document.frame()->domWindow())
     return nullptr;
   Navigator& navigator = *document.frame()->domWindow()->navigator();
   return &from(navigator);
 }
 
 NavigatorServiceWorker& NavigatorServiceWorker::from(Navigator& navigator) {
   NavigatorServiceWorker* supplement = toNavigatorServiceWorker(navigator);
@@ skipping 69 matching lines @@
           "lacks the 'allow-same-origin' flag.";
     } else if (frame->securityContext()->getSecurityOrigin()->hasSuborigin()) {
       errorMessage =
           "Service worker is disabled because the context is in a suborigin.";
     } else {
       errorMessage =
           "Access to service workers is denied in this document origin.";
     }
     return nullptr;
   }
   if (!m_serviceWorker && frame) {

[haraken, 2016/12/12 02:47:51]

nhiroki@: Would you help me understand what this is doing?

- It looks like this code is creating a new ServiceWorkerContainer after a frame
associated with NavigatorServiceWorker gets detached.

- Is the |frame| in this function equal to the frame associated with
NavigatorServiceWorker? I think the answer is no, but it means that
NavigatorServiceWorker is shared among multiple frames (over time). If so, we
will need to clear m_serviceWorker every time the Navigator navigates away to a
new frame. However, the current implementation clears m_serviceWorker only when
the Navigator navigates away from the first frame (because
ContextLifecycleObserver is registered only when NavigatorServiceWorker is
constructed).

     DCHECK(frame->domWindow());
     m_serviceWorker = ServiceWorkerContainer::create(
         frame->domWindow()->getExecutionContext());
   }
   return m_serviceWorker.get();
 }
 
-void NavigatorServiceWorker::contextDestroyed() {
-  m_serviceWorker = nullptr;
-}
-
 DEFINE_TRACE(NavigatorServiceWorker) {
   visitor->trace(m_serviceWorker);
   Supplement<Navigator>::trace(visitor);
-  ContextLifecycleObserver::trace(visitor);
 }
 
 }  // namespace blink