[DevTools] Update media queries when resizing with emulation on.

Media query evaluator assumes that device size cannot change, which is
wrong in emulation mode.

BUG=327641,386142

Review URL: https://codereview.chromium.org/308003007

git-svn-id: svn://svn.chromium.org/blink/trunk@176420 bbb929c8-8fbe-4397-9dbb-9b2b20218538