DevTools: Restore toolbar button order regressed in r175358

The Dock button should be the rightmost one, otherwise it gets overlapped
by a button to its right (Settings).

R=eustas, pfeldman@chromium.org, vsevik
BUG=383313

Review URL: https://codereview.chromium.org/329113002

git-svn-id: svn://svn.chromium.org/blink/trunk@175978 bbb929c8-8fbe-4397-9dbb-9b2b20218538