Correct the null focusedFrame() check in Document

Correct the null focusedFrame() check in Document

Blink revision 170347 introduced a crash because Document::focusedFrame()
fails to check properly for having a null Frame. This corrects the
check.

BUG=358172
R=eseidel@chromium.org, abarth@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170478

[kenrb, 2014-03-31 17:35:43]

Eric or Adam can one of you PTAL? This is a small change to fix a canary crash
that I introduced last week.

[eseidel, 2014-03-31 17:59:58]

lgtm

[commit-bot: I haz the power, 2014-03-31 18:00:00]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kenrb@chromium.org/219453004/1

[commit-bot: I haz the power, 2014-03-31 18:10:39]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-03-31 18:10:40]

Try jobs failed on following builders:
  tryserver.blink on win_blink_compile_dbg

[kenrb, 2014-03-31 18:15:21]

The CQ bit was checked by kenrb@chromium.org

[commit-bot: I haz the power, 2014-03-31 18:15:25]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kenrb@chromium.org/219453004/1

[commit-bot: I haz the power, 2014-03-31 19:18:35]

Change committed as 170478