[Storage] Blob items are now shared between blobs. Ready for disk swap.

storage/browser/blob/shareable_blob_data_item.cc

Index: storage/browser/blob/shareable_blob_data_item.cc
diff --git a/storage/browser/blob/shareable_blob_data_item.cc b/storage/browser/blob/shareable_blob_data_item.cc
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+++ b/storage/browser/blob/shareable_blob_data_item.cc
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+// Copyright (c) 2015 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 "storage/browser/blob/shareable_blob_data_item.h"
+
+#include "storage/browser/blob/blob_data_item.h"
+
+namespace storage {
+
+ShareableBlobDataItem::ShareableBlobDataItem(
+    const std::string& blob_uuid,
+    const scoped_refptr<BlobDataItem>& item)
+    : item_(item) {
+  DCHECK_NE(item_->type(), DataElement::TYPE_BLOB);
+  referencing_blobs_.insert(blob_uuid);
+}
+
+ShareableBlobDataItem::~ShareableBlobDataItem() {
+}
+
+const scoped_refptr<BlobDataItem>& ShareableBlobDataItem::item() {
+  return item_;
+}
+
+}  // namespace storage