Fix 8200: Pressing Esc should cancel dialogs, not commit....

Fix 8200: Pressing Esc should cancel dialogs, not commit.

When we create the OK & Cancel dialog buttons in
DialogClientView, we were registering OK as a handler
for Escape, even though the dialog had a Cancel button.

This is because we register for Esc if the member variable
|cancel_ button_| is NULL. Problem is, that member isn't
created until later on in that function.

We should be checking the |buttons| flags instead.

TEST=Open the Clear Browsing Data dialog, press Tab twice,
press Esc and make sure that the dialog closes and nothing
is cleared (from whatever checkbox was selected).
BUG=8200
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=10631

[jcampan, 2009-02-27 21:02:13]

LGTM