Bug 1558924 - [10.15] Widevine crashes on macOS Catalina Beta r=handyman

Allow limited access to the proc_pidinfo() syscall from the GMP sandbox.

Differential Revision: https://phabricator.services.mozilla.com/D36810

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

security/sandbox/mac/SandboxPolicyGMP.h

@@ -30,6 +30,7 @@ static const char SandboxPolicyGMP[] = R"SANDBOX_LITERAL(
   (moz-deny default)
   ; These are not included in (deny default)
   (moz-deny process-info*)
+  (allow process-info-pidinfo (target self))
   ; This isn't available in some older macOS releases.
   (if (defined? 'nvram*)
     (moz-deny nvram*))