[Time] Half-second delay before clock appears

[hamish]

In the layout-aware time preflet, there is a delay before the clock appears. This seems to happen because the clock dimensions are calculated in FrameResized(), and there is a delay before the view resize message is received.

Moving the dimension calculations to DoLayout() solves this problem.

[hamish]

Fixes clock draw delay #7937

[axeld]

Looks nice, thanks.

[axeld]

Applied in hrev42663.