[Storage] Added tracing for blob creation

storage/browser/blob/blob_url_request_job.h

Index: storage/browser/blob/blob_url_request_job.h
diff --git a/storage/browser/blob/blob_url_request_job.h b/storage/browser/blob/blob_url_request_job.h
index cf296b64cad1183681067aca1f6544fafd7c8560..3dfc093c23676950a59ceb3c3906ac0128671842 100644
--- a/storage/browser/blob/blob_url_request_job.h
+++ b/storage/browser/blob/blob_url_request_job.h
@@ -73,7 +73,7 @@ class STORAGE_EXPORT BlobURLRequestJob
   bool ReadBytesItem(const BlobDataItem& item, int bytes_to_read);
   bool ReadFileItem(FileStreamReader* reader, int bytes_to_read);
 
-  void DidReadFile(int result);
+  void DidReadFile(int chunk_number, int result);
   void DeleteCurrentFileReader();
 
   int ComputeBytesToRead() const;
@@ -114,6 +114,9 @@ class STORAGE_EXPORT BlobURLRequestJob
   bool byte_range_set_;
   net::HttpByteRange byte_range_;
 
+  // Used to create unique id's for tracing.
+  int current_file_chunk_number_;
+
   scoped_ptr<net::HttpResponseInfo> response_info_;
 
   base::WeakPtrFactory<BlobURLRequestJob> weak_factory_;