Add WebRtcDistinctWorkerThread to field trial testing config.

Bug: 1157617
Change-Id: Idc38ef3c6fe98a59a839c1fd5b9c4711302be032
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593117
Auto-Submit: Markus Handell <handellm@google.com>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#838002}

testing/variations/fieldtrial_testing_config.json

@@ -8531,6 +8531,27 @@
             ]
         }
     ],
+    "WebRtcDistinctWorkerThread": [
+        {
+            "platforms": [
+                "windows",
+                "mac",
+                "chromeos",
+                "linux",
+                "ios",
+                "android",
+                "android_weblayer"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "WebRtcDistinctWorkerThread"
+                    ]
+                }
+            ]
+        }
+    ],
     "WebRtcHybridAgc": [
         {
             "platforms": [