Simplify an error condition in requestFullScreenForElement()

Simplify an error condition in requestFullScreenForElement()

Use the existing getter for the top element and do the ancestor test
in a more direct manner.

BUG=383813
R=falken@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178360

[philipj_slow, 2014-07-15 13:17:26]

PTAL.

Depends on https://codereview.chromium.org/390363002/

[falken, 2014-07-17 02:30:24]

neat, lgtm

[philipj_slow, 2014-07-17 08:46:51]

The CQ bit was checked by philipj@opera.com

[commit-bot: I haz the power, 2014-07-17 08:47:18]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/philipj@opera.com/392913002/1

[commit-bot: I haz the power, 2014-07-17 10:16:21]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/17433)

[commit-bot: I haz the power, 2014-07-17 11:25:24]

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

[commit-bot: I haz the power, 2014-07-17 11:25:25]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/17449)

[philipj_slow, 2014-07-17 11:46:48]

Committed patchset #1 manually as r178360 (presubmit successful).