Revert of Telemetry, Mac: Use the actual keychain for performance tes…

…ts. (patchset #1 id:1 of https://codereview.chromium.org/419133002/)

Reason for revert:
Bots need to have their configs updated before this CL can land.

Original issue's description:
> Telemetry, Mac: Use the actual keychain for performance tests.
>
> The real keychain was stubbed out because it was causing problems
> with page cyclers on 10.9 perf bots.
> https://codereview.chromium.org/176583002
>
> This is problematic because it prevents us from catching real performance
> regressions involving the keychain.
> https://code.google.com/p/chromium/issues/detail?id=397308
>
> Rather than disabling keychain interactions altogether, we should fix the 10.9
> page cycler problems. I added a wiki page describing the correct configuration
> for the keychain on Macs.
> https://sites.google.com/a/chromium.org/dev/developers/telemetry/telemetry-mac-keychain-setup
>
> This change will cause a serious performance regression for the telemetry test
> session_restore, and possibly others, since Chrome does not interact well with
> the keychain. See the associated bug. Note that this regression reflects
> accurate user conditions, and that the current performance statistics are
> artifically lowered by stubbing out keychain interactions.
>
> BUG=397308
>
> Committed: https://crrev.com/e38f0dad2e9bdccfaa900e9c2bda2a6e61d85c8b
> Cr-Commit-Position: refs/heads/master@{#302917}

TBR=tonyg@chromium.org,oysteine@chromium.org,jeremy@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=397308

Review URL: https://codereview.chromium.org/681113009

Cr-Commit-Position: refs/heads/master@{#303057}

tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py

@@ -167,6 +167,7 @@ def GetBrowserStartupArgs(self):
     logging.info('Requested remote debugging port: %d' % self._port)
     args.append('--remote-debugging-port=%i' % self._port)
     args.append('--enable-crash-reporter-for-testing')
+    args.append('--use-mock-keychain')
     if not self._is_content_shell:
       args.append('--window-size=1280,1024')
       if self._flash_path: