DevTools: do not scroll console to bottom on resize

Currently console gets scrolled to bottom whenever it gets resized.
The patch fixes this erroneous behavior.

R=vsevik, pfeldman

Review URL: https://codereview.chromium.org/462083002

git-svn-id: svn://svn.chromium.org/blink/trunk@180175 bbb929c8-8fbe-4397-9dbb-9b2b20218538