Reland: Add CertVerifierBuiltin fieldtrial_testing_config for mac.

The 10.15 test expectation for SSLUITest.SHA1IsDefaultDisabled has been
fixed.

Bug: 973650, 1108632
Change-Id: If10c88e4f12c9844dbbc0c28afd1ca9dce4af637
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2324803
Auto-Submit: Matt Mueller <mattm@chromium.org>
Commit-Queue: Brian White <bcwhite@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793603}

testing/variations/fieldtrial_testing_config.json

@@ -1409,6 +1409,21 @@
             ]
         }
     ],
+    "CertVerifierBuiltin": [
+        {
+            "platforms": [
+                "mac"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "CertVerifierBuiltin"
+                    ]
+                }
+            ]
+        }
+    ],
     "ChromeCleanupDistribution": [
         {
             "platforms": [