[Storage] Added tracing for blob creation

storage/browser/blob/blob_data_snapshot.h

 // Copyright 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.
 
 #ifndef STORAGE_BROWSER_BLOB_BLOB_DATA_SNAPSHOT_H_
 #define STORAGE_BROWSER_BLOB_BLOB_DATA_SNAPSHOT_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 19 matching lines @@
 
   const std::vector<scoped_refptr<BlobDataItem>>& items() const {
     return items_;
   }
   const std::string& content_type() const { return content_type_; }
   const std::string& content_disposition() const {
     return content_disposition_;
   }
   size_t GetMemoryUsage() const;
 
+  const std::string& uuid() const { return uuid_; }
+
  private:
   friend class BlobDataBuilder;
   friend class BlobStorageContext;
   BlobDataSnapshot(const std::string& uuid,
                    const std::string& content_type,
                    const std::string& content_disposition);
   BlobDataSnapshot(const std::string& uuid,
                    const std::string& content_type,
                    const std::string& content_disposition,
                    const std::vector<scoped_refptr<BlobDataItem>>& items);
 
   const std::string uuid_;
   const std::string content_type_;
   const std::string content_disposition_;
   // Non-const for constrution in BlobStorageContext
   std::vector<scoped_refptr<BlobDataItem>> items_;
 };
 
 }  // namespace storage
 #endif  // STORAGE_BROWSER_BLOB_BLOB_DATA_SNAPSHOT_H_