DevTools: Overrides section is incompletely shown in developer tools

BUG=313160

TBR=vsevik

Review URL: https://codereview.chromium.org/54103002

git-svn-id: svn://svn.chromium.org/blink/trunk@161024 bbb929c8-8fbe-4397-9dbb-9b2b20218538