Enable iOS SSL committed interstitials in tests

Bug: 987407
Change-Id: Ifb8927a6cfefee1a40b91130677d6ce1b90c3dac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2036544Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Livvie Lin <livvielin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739018}

testing/variations/fieldtrial_testing_config.json

@@ -3018,6 +3018,21 @@
             ]
         }
     ],
+    "IOSSSLCommittedInterstitials": [
+        {
+            "platforms": [
+                "ios"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "SSLCommittedInterstitials"
+                    ]
+                }
+            ]
+        }
+    ],
     "IOSUseWKLoading": [
         {
             "platforms": [