drive: Do not clear dirty bit if someone is writing to the file

Keeping the cache entry dirty to make sure that the edited file will eventually be uploaded.

BUG=326054
TEST=unit_tests

Review URL: https://codereview.chromium.org/139783004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245277 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/chromeos/drive/file_system/update_operation.cc

@@ -95,7 +95,9 @@ FileError UpdateFileLocalState(
   if (drive_file_path->empty())
     return FILE_ERROR_NOT_FOUND;
 
-  // Clear the dirty bit if we have updated an existing file.
+  // Do not clear the dirty bit if someone is writing to the file.
+  if (cache->IsOpenedForWrite(local_id))
+    return FILE_ERROR_OK;
   return cache->ClearDirty(local_id, entry.file_specific_info().md5());
 }