[DevTools] Fix console error when reloading DevTools frontend.
[DevTools] Fix console error when reloading DevTools frontend.

BUG=none

Review URL: https://codereview.chromium.org/1167323004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@196777 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk