Added UsePreferredIntervalForVideo to fieldtrial testing config.

Change-Id: Ie2fe348928333e7a8162fc891fb53d2acb87f574
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1975451
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726673}

testing/variations/fieldtrial_testing_config.json

@@ -7016,6 +7016,21 @@
             ]
         }
     ],
+    "UsePreferredIntervalForVideo": [
+        {
+            "platforms": [
+                "chromeos"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "UsePreferredIntervalForVideo"
+                    ]
+                }
+            ]
+        }
+    ],
     "UseRegistrableDomainInNetworkIsolationKey": [
         {
             "platforms": [