DevTools: [SSP] fix Ctrl-Click navigation over selector

The codemirror got frozen because selection from its
input text area was stolen via "add new property" editing functionality.

BUG=402838
R=apavlov, vsevik

Review URL: https://codereview.chromium.org/476893002

git-svn-id: svn://svn.chromium.org/blink/trunk@180343 bbb929c8-8fbe-4397-9dbb-9b2b20218538