DevTools: bring developer tools window to front when panel gets selected

This patch is a hackish way to bring developer tools front-end to front
whenever Toolbox revealer asks to reveal something.

BUG=399259
R=pfeldman

Review URL: https://codereview.chromium.org/468193002

git-svn-id: svn://svn.chromium.org/blink/trunk@180202 bbb929c8-8fbe-4397-9dbb-9b2b20218538