Add request header on gdata operation for testing ETag match.

chrome/browser/chromeos/drive/drive_file_system.cc

 // Copyright (c) 2012 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_system.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/message_loop_proxy.h"
@@ skipping 1542 matching lines @@
                                  params.mime_type,
                                  REGULAR_FILE);
     return;
   }
 
   // We have enough disk space. Start downloading the file.
   drive_service_->DownloadFile(
       params.virtual_file_path,
       params.local_tmp_path,
       content_url,
+      std::string(),  // ETag
       base::Bind(&DriveFileSystem::OnFileDownloaded,
                  ui_weak_ptr_,
                  params),
       params.get_content_callback);
 }
 
 void DriveFileSystem::GetEntryInfoByPath(const FilePath& file_path,
                                          const GetEntryInfoCallback& callback) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI) ||
          BrowserThread::CurrentlyOn(BrowserThread::IO));
@@ skipping 1446 matching lines @@
     return;
   }
 
   PlatformFileInfoProto entry_file_info;
   DriveEntry::ConvertPlatformFileInfoToProto(*file_info, &entry_file_info);
   *entry_proto->mutable_file_info() = entry_file_info;
   callback.Run(DRIVE_FILE_OK, entry_proto.Pass());
 }
 
 }  // namespace drive