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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

Review URL: https://codereview.chromium.org/576393002

Cr-Commit-Position: refs/heads/master@{#295598}