Mac: Fix accidental changes to fullscreen logic from refactor. (reland)

Mac: Fix accidental changes to fullscreen logic from refactor. (reland)

This CL was reverted due to test failures. Under inspection, the test proved to
already be flaky. The test has been disabled. See http://crbug.com/415422 for
more details.

--------------Original CL Description-----------------

The menu item "Enter Presentation Mode" has different effects in 10.6 and
10.7+. In 10.6, the menu item invokes Immersive Fullscreen. In 10.7+, the menu
item invokes AppKit Fullscreen. Similar logic applies to fullscreen invoked by
an extension.

I accidentally changed this logic during the fullscreen refactor by removing
the 10.6 vs 10.7+ conditional. This CL adds back the conditional. I also
updated the code to explicitly indicate the mechanism that is invoking
fullscreen to prevent similar future mistakes.

Original CL: https://codereview.chromium.org/575653003/

BUG=NONE
TBR=rsesek@chromium.org

Committed: https://crrev.com/dd63d2496e2c6de6ee1ee2f451ddd815d1db5982
Cr-Commit-Position: refs/heads/master@{#295598}

[erikchen, 2014-09-18 21:58:57]

erikchen@chromium.org changed reviewers:
+ rsesek@chromium.org

[erikchen, 2014-09-18 21:58:58]

Relanding this CL after it got reverted.

[erikchen, 2014-09-18 21:59:03]

The CQ bit was checked by erikchen@chromium.org

[commit-bot: I haz the power, 2014-09-18 22:00:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/576393002/1

[commit-bot: I haz the power, 2014-09-18 23:30:23]

Committed patchset #1 (id:1) as dc096b209d8cdd761886ab5f3c4af3550be7f0b2

[commit-bot: I haz the power, 2014-09-18 23:31:12]

Patchset 1 (id:??) landed as
https://crrev.com/dd63d2496e2c6de6ee1ee2f451ddd815d1db5982
Cr-Commit-Position: refs/heads/master@{#295598}