aura: Draw persistent borders around browser windows.

aura: Draw persistent borders around browser windows.

This makes BrowserNonClientFrameViewAura's translucent gray
background always stick out a bit beyond the sides and
bottom of windows, instead of just peeking out when the user
hovers for resizing.

I originally added a separate view for this, but it looked
strange since Chrome already draws a shadow along the top of
the tab strip.

BUG=101977
TEST=manual

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=107823

[James Cook, 2011-10-28 20:41:03]

LGTM

At some point I should correctly compute the top-to-toolbar distance, but that's
my problem not yours. :-)