CPUProfiler: one line fix for warning icon artifact in CPUProfiler grid

BUG=306035
R=alph@chromium.org

Review URL: https://codereview.chromium.org/26815003

git-svn-id: svn://svn.chromium.org/blink/trunk@159326 bbb929c8-8fbe-4397-9dbb-9b2b20218538