File Manager: fix an unsafe const reference (intermittent crash).

Regression started by (http://crrev.com/148492).

The FilePath.BaseName().value() is a local temp object and it is not safe to
assign it to a const string reference. Use the display_name instead.

BUG=139736
TEST=lumpy

Review URL: https://chromiumcodereview.appspot.com/10828086

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@149234 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/chromeos/extensions/file_browser_private_api.cc

@@ -1152,8 +1152,7 @@ void AddMountFunction::GetLocalPathsResponseOnUIThread(
   }
 
   const FilePath& source_path = files[0].local_path;
-  const FilePath::StringType& display_name =
-      files[0].file_path.BaseName().value();
+  const FilePath::StringType& display_name = files[0].display_name;
   // Check if the source path is under GData cache directory.
   gdata::GDataSystemService* system_service =
       gdata::GDataSystemServiceFactory::GetForProfile(profile_);