Update the metrics side bar pane and computed style pane after main frame resize.

The metrics pane showing width and height of the main frame should be updated upon receiving
the resize event. This also applies while docking/undocking the DevTools window.

BUG=322997

Review URL: https://codereview.chromium.org/84643002

git-svn-id: svn://svn.chromium.org/blink/trunk@163004 bbb929c8-8fbe-4397-9dbb-9b2b20218538