Clear Browsing Data should not have a default button

Application Menu:Clear Browsing Data… should not have Clear Browsing Data 
as the default action.  Buttons with destructive actions should never be
the default.

This removes the return key equivalent from the Clear Browsing Data button.
It also adds an escape key equivalent to the Cancel button, so that it will
blink appropriately in response to both escape and command-period.

BUG=21461
TEST=Look and try as above

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=25862

[pink (ping after 24hrs), 2009-09-10 15:00:10]

LGTM