cc: Unify context losing machinery

cc/prioritized_resource.cc

 // Copyright 2012 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 "cc/prioritized_resource.h"
 
 #include "cc/platform_color.h"
 #include "cc/prioritized_resource_manager.h"
 #include "cc/priority_calculator.h"
 #include "cc/proxy.h"
@@ skipping 136 matching lines @@
 {
     DCHECK(!m_owner);
     DCHECK(m_resourceHasBeenDeleted);
 }
 
 void PrioritizedResource::Backing::deleteResource(ResourceProvider* resourceProvider)
 {
     DCHECK(!proxy() || proxy()->isImplThread());
     DCHECK(!m_resourceHasBeenDeleted);
 #ifndef NDEBUG
-    DCHECK(resourceProvider == m_resourceProvider);
+    DCHECK(!resourceProvider || resourceProvider == m_resourceProvider);
 #endif
 
-    resourceProvider->deleteResource(id());
+    if (resourceProvider)
+      resourceProvider->deleteResource(id());
     set_id(0);
     m_resourceHasBeenDeleted = true;
 }
 
 bool PrioritizedResource::Backing::resourceHasBeenDeleted() const
 {
     DCHECK(!proxy() || proxy()->isImplThread());
     return m_resourceHasBeenDeleted;
 }
 
@@ skipping 31 matching lines @@
 }
 
 const Proxy* PrioritizedResource::Backing::proxy() const
 {
     if (!m_owner || !m_owner->resourceManager())
         return 0;
     return m_owner->resourceManager()->proxyForDebug();
 }
 
 }  // namespace cc