gdata: Remove use of FindEntryByPathAsyncOnUI from CreateFileOnUIThread()

chrome/browser/chromeos/gdata/gdata_file_system_interface.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_GDATA_GDATA_FILE_SYSTEM_INTERFACE_H_
 #define CHROME_BROWSER_CHROMEOS_GDATA_GDATA_FILE_SYSTEM_INTERFACE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 239 matching lines @@
                                bool is_exclusive,
                                bool is_recursive,
                                const FileOperationCallback& callback) = 0;
 
   // Creates a file at |file_path|. If the flag |is_exclusive| is true, an
   // error is raised when a file already exists at the path. It is
   // an error if a directory or a hosted document is already present at the
   // path, or the parent directory of the path is not present yet.
   //
   // Can be called from UI/IO thread. |callback| is run on the calling thread
+  // |callback| must not be null.
   virtual void CreateFile(const FilePath& file_path,
                           bool is_exclusive,
                           const FileOperationCallback& callback) = 0;
 
   // Gets |file_path| from the file system. The file entry represented by
   // |file_path| needs to be present in in-memory representation of the file
   // system in order to be retrieved. If the file is not cached, the file
   // will be downloaded through gdata api.
   //
   // Can be called from UI/IO thread. |get_file_callback| and
@@ skipping 85 matching lines @@
                                const FilePath& virtual_dir_path,
                                scoped_ptr<DocumentEntry> entry,
                                const FilePath& file_content_path,
                                GDataCache::FileOperationType cache_operation,
                                const base::Closure& callback) = 0;
 };
 
 }  // namespace gdata
 
 #endif  // CHROME_BROWSER_CHROMEOS_GDATA_GDATA_FILE_SYSTEM_INTERFACE_H_