DevTools: Fix tainted Array methods could crash the debugger.

BUG=364470
R=pfeldman, yurys

Review URL: https://codereview.chromium.org/243853005

git-svn-id: svn://svn.chromium.org/blink/trunk@172049 bbb929c8-8fbe-4397-9dbb-9b2b20218538