Fix typo in TestResultsServer.

TBR=ojan@chromium.org
NOTRY=true
TEST=handlers/testfilehandler_test.py

Review URL: https://codereview.chromium.org/444763002

git-svn-id: svn://svn.chromium.org/blink/trunk@179517 bbb929c8-8fbe-4397-9dbb-9b2b20218538