Garden-o-matic: Make status area drag-resizable by its top border

R=eseidel, dglazkov@chromium.org

Review URL: https://codereview.chromium.org/178193024

git-svn-id: svn://svn.chromium.org/blink/trunk@168687 bbb929c8-8fbe-4397-9dbb-9b2b20218538