Create blobs from Disk Cache entries.

storage/browser/blob/shareable_file_reference.h

 // Copyright (c) 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.
 
 #ifndef STORAGE_BROWSER_BLOB_SHAREABLE_FILE_REFERENCE_H_
 #define STORAGE_BROWSER_BLOB_SHAREABLE_FILE_REFERENCE_H_
 
-#include <vector>
-
+#include "storage/browser/blob/blob_data_item.h"
 #include "storage/browser/blob/scoped_file.h"
 #include "storage/browser/storage_browser_export.h"
 
 namespace storage {
 
 // ShareableFileReference allows consumers to share FileReference for the
 // same path if it already exists in its internal map.
 // This class is non-thread-safe and all methods must be called on a single
 // thread.
-class STORAGE_EXPORT ShareableFileReference
-    : public base::RefCounted<ShareableFileReference> {
+// This class inherits directly from BlobDataItem::DataHandle as an optimization
+// to remove double-dereferences from refcounting the DataHandle objects. This
+// only works because there are no other fields in the DataHandle.

[michaeln, 2015/06/12 23:43:06]

I don't think the editorial comments about dbl-derefs and no other fields are
helpful? Why say anything, the derivation says it all.

[dmurph, 2015/06/13 00:09:43]

I asked him to add this in case it wasn't clear for new readers. But it can
definitely be removed if you think it's obvious.

[gavinp, 2015/06/15 14:01:19]

Removed, just because I'm slightly with michaeln here. Let me know if you guys
decide it should be back! :)

+class STORAGE_EXPORT ShareableFileReference : public BlobDataItem::DataHandle {
  public:
   typedef ScopedFile::ScopeOutCallback FinalReleaseCallback;
 
   enum FinalReleasePolicy {
     DELETE_ON_FINAL_RELEASE = ScopedFile::DELETE_ON_SCOPE_OUT,
     DONT_DELETE_ON_FINAL_RELEASE = ScopedFile::DONT_DELETE_ON_SCOPE_OUT,
   };
 
   // Returns a ShareableFileReference for the given path, if no reference
   // for this path exists returns NULL.
@@ skipping 22 matching lines @@
 
   // The full file path.
   const base::FilePath& path() const { return scoped_file_.path(); }
 
   // The |callback| is fired when the final reference of this instance
   // is released. If release policy is DELETE_ON_FINAL_RELEASE the
   // callback task(s) is/are posted before the deletion is scheduled.
   void AddFinalReleaseCallback(const FinalReleaseCallback& callback);
 
  private:
-  friend class base::RefCounted<ShareableFileReference>;
-
   ShareableFileReference(ScopedFile scoped_file);
-  ~ShareableFileReference();
+  ~ShareableFileReference() override;
 
   ScopedFile scoped_file_;
 
   DISALLOW_COPY_AND_ASSIGN(ShareableFileReference);
 };
 
 }  // namespace storage
 
 #endif  // STORAGE_BROWSER_BLOB_SHAREABLE_FILE_REFERENCE_H_