[fsp] Buffer consecutive Write() calls.

storage/browser/fileapi/file_stream_writer.h

Index: storage/browser/fileapi/file_stream_writer.h
diff --git a/storage/browser/fileapi/file_stream_writer.h b/storage/browser/fileapi/file_stream_writer.h
index ec59ec0f84d6111826c95dab54f2761a3c66044c..c0771002ffa7d1a8d62e6d5d0220203163265c5f 100644
--- a/storage/browser/fileapi/file_stream_writer.h
+++ b/storage/browser/fileapi/file_stream_writer.h
@@ -46,6 +46,10 @@ class FileStreamWriter {
   // callback will be run on the thread where Write() was called when the write
   // has completed.
   //
+  // After the last write, Flush() must be called unless the flushing on
+  // completion is explicitly disabled for the file system type, the writer is
+  // created for. See FileSystemContext::ShouldFlushOnWriteCompletion().
+  //
   // This errors out (either synchronously or via callback) with:
   //   net::ERR_FILE_NOT_FOUND: When the target file is not found.
   //   net::ERR_ACCESS_DENIED: When the target file is a directory or