DevTools: Fix regression in canvas profiler.

BUG=367117
R=dgozman@chromium.org, dgozman, pfeldman

Review URL: https://codereview.chromium.org/258693005

git-svn-id: svn://svn.chromium.org/blink/trunk@172639 bbb929c8-8fbe-4397-9dbb-9b2b20218538