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

chrome/browser/chromeos/file_system_provider/fileapi/buffering_file_stream_reader.h

Index: chrome/browser/chromeos/file_system_provider/fileapi/buffering_file_stream_reader.h
diff --git a/chrome/browser/chromeos/file_system_provider/fileapi/buffering_file_stream_reader.h b/chrome/browser/chromeos/file_system_provider/fileapi/buffering_file_stream_reader.h
index e0e4eccb901476e522c23a68c53a83c948ad8aa6..627a76352e51e93b462bee2e1eb629941a2fe70e 100644
--- a/chrome/browser/chromeos/file_system_provider/fileapi/buffering_file_stream_reader.h
+++ b/chrome/browser/chromeos/file_system_provider/fileapi/buffering_file_stream_reader.h
@@ -20,16 +20,19 @@ namespace file_system_provider {
 
 // Wraps the file stream reader implementation with a prefetching buffer.
 // Reads data from the internal file stream reader in chunks of size at least
-// |buffer_size| bytes (or less for the last chunk, because of EOF).
+// |preloading_buffer_length| bytes (or less for the last chunk, because of
+// EOF). If total number of bytes to be downloaded is known, it should be passed
+// as |bytes_to_read|, otherwise it must be -1.
 //
-// The underlying inner file stream reader *must not* return any values
+// The underlying internal file stream reader *must not* return any values
 // synchronously. Instead, results must be returned by a callback, including
 // errors.
 class BufferingFileStreamReader : public storage::FileStreamReader {
  public:
   BufferingFileStreamReader(
       scoped_ptr<storage::FileStreamReader> file_stream_reader,
-      int buffer_size);
+      int preloading_buffer_length,
+      int64 bytes_to_read);
 
   virtual ~BufferingFileStreamReader();
 
@@ -49,6 +52,8 @@ class BufferingFileStreamReader : public storage::FileStreamReader {
   // Preloads data from the internal stream reader and calls the |callback|.
   void Preload(const net::CompletionCallback& callback);
 
+  void OnReadCompleted(const net::CompletionCallback& callback, int result);
+
   // Called when preloading of a buffer chunk is finished. Updates state of the
   // preloading buffer and copied requested data to the |buffer|.
   void OnPreloadCompleted(scoped_refptr<net::IOBuffer> buffer,
@@ -57,10 +62,12 @@ class BufferingFileStreamReader : public storage::FileStreamReader {
                           int result);
 
   scoped_ptr<storage::FileStreamReader> file_stream_reader_;
-  int buffer_size_;
+  int preloading_buffer_length_;
+  int64 bytes_to_read_;
+  int64 bytes_read_;
   scoped_refptr<net::IOBuffer> preloading_buffer_;
   int preloading_buffer_offset_;
-  int buffered_bytes_;
+  int preloaded_bytes_;
 
   base::WeakPtrFactory<BufferingFileStreamReader> weak_ptr_factory_;
   DISALLOW_COPY_AND_ASSIGN(BufferingFileStreamReader);