Fix crash in GeolocationController when the page gets destroyed

Source/modules/geolocation/GeolocationController.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 46 matching lines @@
     // This may be called multiple times with the same observer, though removeObserver()
     // is called only once with each.
     bool wasEmpty = m_observers.isEmpty();
     m_observers.add(observer);
     if (enableHighAccuracy)
         m_highAccuracyObservers.add(observer);
 
     if (m_client) {
         if (enableHighAccuracy)
             m_client->setEnableHighAccuracy(true);
-        if (wasEmpty && page()->visibilityState() == PageVisibilityStateVisible)
+        if (wasEmpty && page() && page()->visibilityState() == PageVisibilityStateVisible)
             m_client->startUpdating();
     }
 }
 
 void GeolocationController::removeObserver(Geolocation* observer)
 {
     if (!m_observers.contains(observer))
         return;
 
     m_observers.remove(observer);
@@ skipping 50 matching lines @@
         return 0;
 
     return m_client->lastPosition();
 }
 
 void GeolocationController::pageVisibilityChanged()
 {
     if (m_observers.isEmpty() || !m_client)
         return;
 
-    if (page()->visibilityState() == PageVisibilityStateVisible)
+    if (page() && page()->visibilityState() == PageVisibilityStateVisible)

[adamk, 2013/10/23 15:34:38]

I'd hope that page() couldn't be null here, since this callback should be coming
from an instance of Page, but checking it is harmless enough.

         m_client->startUpdating();
     else
         m_client->stopUpdating();
 }
 
 const char* GeolocationController::supplementName()
 {
     return "GeolocationController";
 }
 
 void provideGeolocationTo(Page* page, GeolocationClient* client)
 {
     Supplement<Page>::provideTo(page, GeolocationController::supplementName(), GeolocationController::create(page, client));
 }
 
 } // namespace WebCore