gdata: Remove use of FindEntryByPathAsyncOnUI from CreateFileOnUIThread()

chrome/browser/chromeos/gdata/gdata_file_system_interface.h

Index: chrome/browser/chromeos/gdata/gdata_file_system_interface.h
diff --git a/chrome/browser/chromeos/gdata/gdata_file_system_interface.h b/chrome/browser/chromeos/gdata/gdata_file_system_interface.h
index 046fde4e71321734969b7c4a2f10ea3cbb4eaa40..912ea50c888b0fa0b45c418a6b3fcaf5cfe5f048 100644
--- a/chrome/browser/chromeos/gdata/gdata_file_system_interface.h
+++ b/chrome/browser/chromeos/gdata/gdata_file_system_interface.h
@@ -257,6 +257,7 @@ class GDataFileSystemInterface {
   // 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;