DevTools: Fix Ctrl+G dialog caret positioning at the end of input

This was broken as a result of r177724 fixing a different issue.

R=vsevik
BUG=393888
NOTRY=true

Review URL: https://codereview.chromium.org/387393003

git-svn-id: svn://svn.chromium.org/blink/trunk@178160 bbb929c8-8fbe-4397-9dbb-9b2b20218538