Fix sorting by flakiness in the flakiness dashboard.

At some point, the property getting set changed from flips to flipCount.

R=eseidel@google.com

Review URL: https://codereview.chromium.org/25608002

git-svn-id: svn://svn.chromium.org/blink/trunk@158659 bbb929c8-8fbe-4397-9dbb-9b2b20218538