Enabling perfbot testing for ImportantSiteInCBD

R=motek@chromium.org,rkaplow@chromium.org
BUG=579763

Review-Url: https://codereview.chromium.org/2143113002
Cr-Commit-Position: refs/heads/master@{#406705}

testing/variations/fieldtrial_testing_config_android.json

@@ -131,6 +131,14 @@
             "group_name": "Enabled"
         }
     ],
+    "ImportantSitesInCBD": [
+        {
+            "enable_features": [
+                "ImportantSitesInCBD"
+            ],
+            "group_name": "DialogEnabled"
+        }
+    ],
     "InvalidationsGCMUpstream": [
         {
             "group_name": "Enabled"