Add an utility interface ReaderProxy and its implementation for local file.

chrome/browser/chromeos/drive/drive_file_stream_reader.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/drive/drive_file_stream_reader.h"
 
 #include "base/logging.h"
+#include "content/public/browser/browser_thread.h"
+#include "net/base/file_stream.h"
+#include "net/base/io_buffer.h"
+
+using content::BrowserThread;
 
 namespace drive {
+namespace internal {
+
+LocalReaderProxy::LocalReaderProxy(scoped_ptr<net::FileStream> file_stream)
+    : file_stream_(file_stream.Pass()) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  DCHECK(file_stream_);
+}
+
+LocalReaderProxy::~LocalReaderProxy() {
+}
+
+int LocalReaderProxy::Read(net::IOBuffer* buffer, int buffer_length,
+                           const net::CompletionCallback& callback) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  DCHECK(file_stream_);
+  return file_stream_->Read(buffer, buffer_length, callback);
+}
+
+void LocalReaderProxy::OnGetContent(scoped_ptr<std::string> data) {
+  // This method should never be called, because no data should be received
+  // from the network during the reading of local-cache file.
+  NOTREACHED();
+}
+
+void LocalReaderProxy::OnError(DriveFileError error) {
+  // This method should never be called, because we don't access to the server
+  // during the reading of local-cache file.
+  NOTREACHED();
+}
+
+}  // namespace internal
+
 
 DriveFileStreamReader::DriveFileStreamReader() {
 }
 
 DriveFileStreamReader::~DriveFileStreamReader() {
 }
 
 int DriveFileStreamReader::Read(net::IOBuffer* buf, int buf_len,
                                 const net::CompletionCallback& callback) {
   // TODO(hidehiko): Implement this.
   NOTIMPLEMENTED();
   return 0;
 }
 
 int64 DriveFileStreamReader::GetLength(
     const net::Int64CompletionCallback& callback) {
   // TODO(hidehiko): Implement this.
   NOTIMPLEMENTED();
   return 0;
 }
 
 }  // namespace drive