DevTools: [Regression] Invalid button glyphs in the responsive design pane.

BUG=434650
NOTRY=true

Review URL: https://codereview.chromium.org/736973002

git-svn-id: svn://svn.chromium.org/blink/trunk@185645 bbb929c8-8fbe-4397-9dbb-9b2b20218538