DevTools: Rename DOMCounter* -> Counter* in the frontend

Namely: DOMCounterUI, DOMCountersGraph

Review URL: https://codereview.chromium.org/122223002

git-svn-id: svn://svn.chromium.org/blink/trunk@164378 bbb929c8-8fbe-4397-9dbb-9b2b20218538