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

webkit/browser/fileapi/file_system_backend.h

Index: webkit/browser/fileapi/file_system_backend.h
diff --git a/webkit/browser/fileapi/file_system_backend.h b/webkit/browser/fileapi/file_system_backend.h
index b71c8cab06d7fce114b06a3ade098dff8084f165..9fbdc359129701a523e191a87ef1e895e447a715 100644
--- a/webkit/browser/fileapi/file_system_backend.h
+++ b/webkit/browser/fileapi/file_system_backend.h
@@ -35,6 +35,10 @@ class FileSystemOperation;
 class FileSystemQuotaUtil;
 class WatcherManager;
 
+// Maximum value of length arguments used for

[hashimoto, 2014/09/05 03:17:27]

There is no longer |length| argument.

[mtomasz, 2014/09/05 05:31:42]

Done.

+// FileSystemBackend::CreateFileStreamReader().
+const int64 kMaximumLength = std::numeric_limits<int64>::max();
+
 // An interface for defining a file system backend.
 //
 // NOTE: when you implement a new FileSystemBackend for your own
@@ -108,12 +112,12 @@ class STORAGE_EXPORT FileSystemBackend {
   // if it does any succeeding read operations should fail with
   // ERR_UPLOAD_FILE_CHANGED error.
   // This method itself does *not* check if the given path exists and is a
-  // regular file.
-  // 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.
+  // regular file. At most |max_bytes_to_read| can be fetched from the file
+  // stream reader.
   virtual scoped_ptr<storage::FileStreamReader> CreateFileStreamReader(
       const FileSystemURL& url,
       int64 offset,
+      int64 max_bytes_to_read,
       const base::Time& expected_modification_time,
       FileSystemContext* context) const = 0;