Add fieldtrial_testing_config for CertVerifierBuiltin on Linux

Bug: 973650
Change-Id: I87468a94853789b2cc30fbc70d3bba20d89634b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1853908
Commit-Queue: Matt Mueller <mattm@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706572}

testing/variations/fieldtrial_testing_config.json

@@ -1511,6 +1511,19 @@
                     ]
                 }
             ]
+        },
+        {
+            "platforms": [
+                "linux"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled_V2",
+                    "enable_features": [
+                        "CertVerifierBuiltin"
+                    ]
+                }
+            ]
         }
     ],
     "ChromeCleanupDistribution": [