ChromeOS: Fix DCHECK failure after file copying in Drive folder.

This is due to multiple callback calls in GDataFileSystem::AddUploadedFileToCache.
It should be called exactly once on every code path.

BUG=none
TEST=Manual: open Drive folder, select a file, ctrl-C and then ctrl-V.

Review URL: https://chromiumcodereview.appspot.com/10834328

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@151713 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/chromeos/gdata/gdata_file_system.cc

@@ -3083,8 +3083,11 @@ void GDataFileSystem::AddUploadedFileToCache(
                                             params->callback));
   } else {
     NOTREACHED() << "Unexpected upload mode: " << params->upload_mode;
+    // Shouldn't reach here, so the line below should not make much sense, but
+    // since calling |callback| exactly once is our obligation, we'd better call
+    // it for not to clutter further more.
+    params->callback.Run();
   }
-  params->callback.Run();
 }
 
 void GDataFileSystem::Observe(int type,