Revert 285173 "Removed InProcessBrowserTest::CleanUpOnMainThread()"

Revert 285173 "Removed InProcessBrowserTest::CleanUpOnMainThread()"

suspected to have broken ChromeOS browsertests:

SessionRestoreTestChromeOS.RestoreAppsV1
SessionRestoreTestChromeOS.RestoreBrowserWindows
SessionRestoreTestChromeOS.RestoreMaximized

Sample failure output:

SessionRestoreTestChromeOS.RestoreBrowserWindows (run #1):
[ RUN      ] SessionRestoreTestChromeOS.RestoreBrowserWindows
[7235:7235:0724/051700:WARNING:chrome_browser_main_chromeos.cc(275)] Running as stub user with profile dir: test-user
Xlib:  extension "RANDR" missing on display ":9".
[7235:7377:0724/051700:WARNING:local_extension_cache.cc(199)] Extensions will not be installed from update URLs until /var/cache/external_cache/.initialized exists.
../../chrome/browser/sessions/session_restore_browsertest_chromeos.cc:118: Failure
Value of: total_count
  Actual: 1
Expected: 2u
Which is: 2
[7235:7331:0724/051701:WARNING:raw_channel_posix.cc(214)] recvmsg: Connection reset by peer
[  FAILED  ] SessionRestoreTestChromeOS.RestoreBrowserWindows, where TypeParam =  and GetParam() =  (827 ms)

> Removed InProcessBrowserTest::CleanUpOnMainThread()
>
> Changed all instances of superfluous InProcessBrowserTest::CleanUpOnMainThread()
> API to use BrowserTestBase::TearDownOnMainThread() instead.
>
> BUG=381181
> TBR=rockot@chromium.org,sky@chromium.org,nkostylev@chromium.org
>
> Review URL: https://codereview.chromium.org/366813007

TBR=atwilson@chromium.org

Review URL: https://codereview.chromium.org/415133002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285278 0039d316-1c4b-4281-b951-d872f2087c98