Add fieldtrial_testing_config for CertVerifierBuiltin chromeos

Bug: 973650
Change-Id: I44a49aa98ba3e35a5f4edff9e60fa16d7948d5a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674443
Commit-Queue: Matt Mueller <mattm@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697312}

testing/variations/fieldtrial_testing_config.json

@@ -1517,6 +1517,21 @@
             ]
         }
     ],
+    "CertVerifierBuiltin": [
+        {
+            "platforms": [
+                "chromeos"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "CertVerifierBuiltin"
+                    ]
+                }
+            ]
+        }
+    ],
     "ChromeCleanupDistribution": [
         {
             "platforms": [