DevTools: Place styles sidebar toolbar correctly so that it could receive mouse events.
DevTools: Place styles sidebar toolbar correctly so that it could receive mouse events.

BUG=280032

Review URL: https://chromiumcodereview.appspot.com/23680006

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@156848 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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