Bug 1552425 - re-disable e10s when generating PGO profile data to fix speedometer perf regression r=froydnj

Bug 1548941 restricted under which circumstances we allow the
browser.tabs.remote.autostart pref to turn off e10s. The PGO profileserver.py
script relied on the unittest-required user.js prefs collection to turn off
e10s (see also bug 1196094) via this pref. For PGO builds, we do not set the
MOZ_DISABLE_NONLOCAL_CONNECTIONS env var, which meant that we stopped
honouring the pref to turn off e10s. Unfortunately, this meant that
e10s was inadvertently now switched on for the pgo profiling, which
negatively impacted speedometer on PGO builds (and possibly other tests).

All this change does is re-disable e10s for PGO profiling. We should
investigate how to turn e10s on "properly" for PGO, but we can do that in
bug 1196094, without taking this temporary regression, especially as 68
branches.

Differential Revision: https://phabricator.services.mozilla.com/D31736

--HG--
extra : moz-landing-system : lando

build/pgo/profileserver.py

@@ -80,6 +80,10 @@ if __name__ == '__main__':
         env = os.environ.copy()
         env["MOZ_CRASHREPORTER_NO_REPORT"] = "1"
         env["XPCOM_DEBUG_BREAK"] = "warn"
+        # TODO should use e10s and gather data from all processes (bug 1196094).
+        # Note that unittest-required/user.js sets the autostart pref, but it
+        # is ignored by the code in nsAppRunner.
+        env["MOZ_FORCE_DISABLE_E10S"] = "1"
 
         # For VC12+, make sure we can find the right bitness of pgort1x0.dll
         if not substs.get('HAVE_64BIT_BUILD'):