Revert of Fix Windows logoff race.

Revert of Fix Windows logoff race. (https://codereview.chromium.org/349263004/)

Reason for revert:
Suspected as cause of browser_tests failures on Mac10.7 Tests:

http://build.chromium.org/p/chromium.mac/builders/Mac10.7%20Tests%20%283%29/builds/28572

ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession (run #1):
[ RUN      ] ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession
[10963:519:0708/084058:ERROR:browser_process_impl.cc(495)] Not implemented reached in virtual void BrowserProcessImpl::EndSession()
../../chrome/browser/profiles/profile_browsertest.cc:365: Failure
Value of: "SessionEnded"
Expected: GetExitTypePreferenceFromDisk(profile)
Which is: "Crashed"
[  FAILED  ] ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession, where TypeParam =  and GetParam() =  (780 ms)

ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession (run #2):
[ RUN      ] ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession
[12926:519:0708/084834:ERROR:browser_process_impl.cc(495)] Not implemented reached in virtual void BrowserProcessImpl::EndSession()
../../chrome/browser/profiles/profile_browsertest.cc:365: Failure
Value of: "SessionEnded"
Expected: GetExitTypePreferenceFromDisk(profile)
Which is: "Crashed"
[  FAILED  ] ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession, where TypeParam =  and GetParam() =  (639 ms)

ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession (run #3):
[ RUN      ] ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession
[12935:519:0708/084836:ERROR:browser_process_impl.cc(495)] Not implemented reached in virtual void BrowserProcessImpl::EndSession()
../../chrome/browser/profiles/profile_browsertest.cc:365: Failure
Value of: "SessionEnded"
Expected: GetExitTypePreferenceFromDisk(profile)
Which is: "Crashed"
[  FAILED  ] ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession, where TypeParam =  and GetParam() =  (551 ms)

ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession (run #4):
[ RUN      ] ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession
[12937:519:0708/084837:ERROR:browser_process_impl.cc(495)] Not implemented reached in virtual void BrowserProcessImpl::EndSession()
../../chrome/browser/profiles/profile_browsertest.cc:365: Failure
Value of: "SessionEnded"
Expected: GetExitTypePreferenceFromDisk(profile)
Which is: "Crashed"
[  FAILED  ] ProfileBrowserTest.WritesProfilesSynchronouslyOnEndSession, where TypeParam =  and GetParam() =  (560 ms)

Original issue's description:
> Fix Windows logoff race by posting a sentinel task to each taskrunner used to save state, and blocking on the completion of all sentinels.
> De-flake and re-enable ProfileBrowserTests, by not running the tasks queued to initialize Bookmarks. This caused test failures when the delayed initialization managed to run.
> This depends on https://codereview.chromium.org/370323002/, which fixes a BookmarkStorage lifetime issue, and https://codereview.chromium.org/375683002/ which annotates a remaining leak.
> 
> TBR=sky@chromium.org, brettw@chromium.org
> 
> R=erikwright@chromium.org, gab=chromium.org, brettw@chromium.org
> BUG=386126, 141141, 141517, 142787, 140882, 165760, 163713, 391508
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=281746

TBR=siggi
BUG=392186
NOTREECHECKS=true
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=281766

[maniscalco, 2014-07-08 16:17:35]

Created Revert of Fix Windows logoff race.

[commit-bot: I haz the power, 2014-07-08 16:19:13]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/maniscalco@chromium.org/378863003/1

[commit-bot: I haz the power, 2014-07-08 16:19:13]

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

[commit-bot: I haz the power, 2014-07-08 16:19:17]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[maniscalco, 2014-07-08 16:24:07]

siggi, I put you on the TBR line.

[maniscalco, 2014-07-08 16:24:10]

The CQ bit was checked by maniscalco@chromium.org

[commit-bot: I haz the power, 2014-07-08 16:25:23]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/maniscalco@chromium.org/378863003/1

[commit-bot: I haz the power, 2014-07-08 16:27:18]

Change committed as 281766