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

chrome/browser/chromeos/drive/drive_file_stream_reader.cc

Index: chrome/browser/chromeos/drive/drive_file_stream_reader.cc
diff --git a/chrome/browser/chromeos/drive/drive_file_stream_reader.cc b/chrome/browser/chromeos/drive/drive_file_stream_reader.cc
index 80aaac7cf5d1ce208df1bb34e333e96eb8c46abd..17d21c4ce8df5411157d975c94a0a07fb332b6a3 100644
--- a/chrome/browser/chromeos/drive/drive_file_stream_reader.cc
+++ b/chrome/browser/chromeos/drive/drive_file_stream_reader.cc
@@ -5,8 +5,45 @@
 #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() {
 }