DevTools: Better position suggest box.

This patch also makes TextEditor SuggestBox to be correctly aligned with the text.

R=lushnikov, pfeldman, apavlov

Review URL: https://codereview.chromium.org/246063007

git-svn-id: svn://svn.chromium.org/blink/trunk@172367 bbb929c8-8fbe-4397-9dbb-9b2b20218538