Sheriff-o-matic should have an awesome transition

This CL makes the sheriff-o-matic pages slide in from the side when you examine
failures or change tabs.

R=eseidel@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/392093002

git-svn-id: svn://svn.chromium.org/blink/trunk@178221 bbb929c8-8fbe-4397-9dbb-9b2b20218538