Implement the renderer side of the mojo based local storage implementation.

content/renderer/dom_storage/local_storage_cached_areas.h

 // Copyright 2016 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 CONTENT_RENDERER_DOM_STORAGE_LOCAL_STORAGE_CACHED_AREAS_H_
 #define CONTENT_RENDERER_DOM_STORAGE_LOCAL_STORAGE_CACHED_AREAS_H_
 
 #include <map>
 
 #include "base/macros.h"
-#include "base/memory/ref_counted.h"
 #include "url/origin.h"
 
 namespace content {
 class LocalStorageCachedArea;
 class StoragePartitionService;
 
 // Owns all the LocalStorageCachedArea objects in a renderer. This is needed
 // because we can have n LocalStorageArea objects for the same origin but we
 // want just one LocalStorageCachedArea to service them (no point in having
 // multiple caches of the same data in the same process).
 class LocalStorageCachedAreas {
  public:
   explicit LocalStorageCachedAreas(
       StoragePartitionService* storage_partition_service);
   ~LocalStorageCachedAreas();
 
-  scoped_refptr<LocalStorageCachedArea> GetLocalStorageCachedArea(
-      const url::Origin& origin);
+  // Returns, creating if necessary, a cached storage area for the given origin.
+  // The object owns itself, and self-destructs when there no storage areas for
+  // the origin left.
+  LocalStorageCachedArea* GetLocalStorageCachedArea(const url::Origin& origin);

[michaeln, 2016/03/18 01:05:17]

naming nit: since these are in a class named LocalStorageCachedAreas, you could
use shorter method names... maybe OpenCachedArea/CacheAreaClosed()

[jam, 2016/03/18 16:48:33]

Done.

 
   // Called by LocalStorageCachedArea on destruction.
   void LocalStorageCacheAreaClosed(LocalStorageCachedArea* cached_area);
 
  private:
   StoragePartitionService* const storage_partition_service_;

[michaeln, 2016/03/18 01:05:17]

I'm a wary about the assumption that Blink is well behaved and will actually
delete all of the WebStorageAreas prior to Shutdown() and/or at least not invoke
or delete any after Shutdown() has been called.

Having been burned by shutdown bugs too many time, i'd rather defend against the
unexpected in that regard. I have little confidence that  ~WebStorageArea()
cant/wont happen after ~LocalStorageCachedAreas() in some crazy cases.

Maybe have the backptrs be WeakPtrs?

[jam, 2016/03/18 16:48:33]

in this specific case, I prefer to not do this unless we see crashes. the reason
is that LocalStorageCachedAreas is owned by the blink platform impl. that is
alive for the lifetime of the renderer process (owned by RenderThread). so i
don't see how that could happen.

note that this code will all move to blink once it's working, so hopefully that
decreases the chance that there's different assumptions.

 
   // Maps from an origin to its LocalStorageCachedArea object. The object owns
   // itself.
   std::map<url::Origin, LocalStorageCachedArea*> cached_areas_;
 
   DISALLOW_COPY_AND_ASSIGN(LocalStorageCachedAreas);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_DOM_STORAGE_LOCAL_STORAGE_CACHED_AREAS_H_