Revert of Add support for backgrounding processes on the Mac

Revert of Add support for backgrounding processes on the Mac (patchset #22 id:420001 of https://codereview.chromium.org/989703002/)

Reason for revert:
This CL seems to be the cause of ExtensionApiNewTabTest.Tabs failures on Mac.

Original issue's description:
> Add support for backgrounding processes on the Mac
>
> Added process_mac.cc with implementations of IsProcessBackgrounded() and
> SetProcessBackgrounded().
>
> BUG=460102
>
> Originally Committed: https://crrev.com/e3bb10f7860a1d553c85293bd7d7615c0e7f0fd9
> Reverted: https://crrev.com/ce6226a7ffe2c1cb7ac5f6cf34b56b8d217686b9
>
> Committed: https://crrev.com/0160d130f8a4462fa7bfb8a9924e476d31ba9a48
> Cr-Commit-Position: refs/heads/master@{#330464}

TBR=rsesek@chromium.org,gab@chromium.org,thakis@chromium.org,asvitkine@chromium.org,avi@chromium.org,kbr@chromium.org,shrike@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=460102
Committed: https://crrev.com/93ef7cd278d450b06f4a95fad6577d05b67624aa
Cr-Commit-Position: refs/heads/master@{#330519}

[Thiemo Nagel, 2015-05-19 14:25:49]

Created Revert of Add support for backgrounding processes on the Mac

[commit-bot: I haz the power, 2015-05-19 14:26:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1142913004/1

[commit-bot: I haz the power, 2015-05-19 14:26:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-19 14:27:53]

Patchset 1 (id:??) landed as
https://crrev.com/93ef7cd278d450b06f4a95fad6577d05b67624aa
Cr-Commit-Position: refs/heads/master@{#330519}