DevTools: [MQI] min-width css-breakpoints label "sticking"

This patch adds min-width label "sticking" for css breakpoints labels
in Media Query Inspector. The situation like this might occur whenever
inspected site gets page scaling and scrolling.

BUG=382996
R=pfeldman, dgozman

Review URL: https://codereview.chromium.org/363343002

git-svn-id: svn://svn.chromium.org/blink/trunk@177526 bbb929c8-8fbe-4397-9dbb-9b2b20218538