[BlobAsync] Disk support for blob storage

storage/browser/blob/shareable_blob_data_item.h

Index: storage/browser/blob/shareable_blob_data_item.h
diff --git a/storage/browser/blob/shareable_blob_data_item.h b/storage/browser/blob/shareable_blob_data_item.h
index 4c2f9c1833262d18dfa82b622abdfef8585b9541..fd5e7212e825d97ae99e810df1b9c38a59bae275 100644
--- a/storage/browser/blob/shareable_blob_data_item.h
+++ b/storage/browser/blob/shareable_blob_data_item.h
@@ -23,22 +23,27 @@ class InternalBlobData;
 // The data in this class (the item) is immutable, but the item itself can be
 // swapped out with an item with the same data but a different backing (think
 // RAM vs file backed).
-class ShareableBlobDataItem : public base::RefCounted<ShareableBlobDataItem> {
+class ShareableBlobDataItem
+    : public base::RefCountedThreadSafe<ShareableBlobDataItem> {

[michaeln, 2016/07/07 20:05:22]

Why does this need to be a threadsafe refcount? If this really is needed, seems
like BlobDataItem might also need a threadsafe refcount.

  public:
-  ShareableBlobDataItem(const std::string& blob_uuid,
-                        const scoped_refptr<BlobDataItem>& item);
+  ShareableBlobDataItem(uint64_t item_id, scoped_refptr<BlobDataItem> item);
 
   const scoped_refptr<BlobDataItem>& item();
 
+  uint64_t item_id() { return item_id_; }
+
   base::hash_set<std::string>& referencing_blobs() {
     return referencing_blobs_;
   }
 
  private:
-  friend class base::RefCounted<ShareableBlobDataItem>;
+  friend class base::RefCountedThreadSafe<ShareableBlobDataItem>;
   friend class InternalBlobData;
+  friend class BlobMemoryController;
   ~ShareableBlobDataItem();
 
+  // This is a unique identifier for this ShareableBlobDataItem.
+  uint64_t item_id_;
   scoped_refptr<BlobDataItem> item_;
 
   base::hash_set<std::string> referencing_blobs_;