[fsp] Improve performance for reading small chunks of data.

webkit/browser/fileapi/file_system_context.h

Index: webkit/browser/fileapi/file_system_context.h
diff --git a/webkit/browser/fileapi/file_system_context.h b/webkit/browser/fileapi/file_system_context.h
index bcae2ff138182687ec4cad00fb511f9f7ee12544..d93e67c0ab5f4081ff6666b2dbcb391701a9db01 100644
--- a/webkit/browser/fileapi/file_system_context.h
+++ b/webkit/browser/fileapi/file_system_context.h
@@ -246,9 +246,12 @@ class WEBKIT_STORAGE_BROWSER_EXPORT FileSystemContext
   // FileSystemBackend for the URL and call the backend's CreateFileReader.
   // The resolved FileSystemBackend could perform further specialization
   // depending on the filesystem type pointed by the |url|.
+  // The |length| argument says how many bytes are going to be read using the
+  // instance of the file stream reader. If unknown, then equal to -1.
   scoped_ptr<storage::FileStreamReader> CreateFileStreamReader(
       const FileSystemURL& url,
       int64 offset,
+      int64 length,
       const base::Time& expected_modification_time);
 
   // Creates new FileStreamWriter instance to write into a file pointed by