[blink scheduler] Add OptOutWebRTCFromAllThrottling to testing config.

This is a pre-requisite for Beta and Stable experiments.

Bug: 1101731
Change-Id: Ib127de8a4e67b2ea55b87b6053ce2ae4673566be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2364819Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800671}

testing/variations/fieldtrial_testing_config.json

@@ -4746,6 +4746,27 @@
             ]
         }
     ],
+    "OptOutWebRTCFromAllThrottling": [
+        {
+            "platforms": [
+                "android",
+                "android_weblayer",
+                "android_webview",
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "OptOutWebRTCFromAllThrottling"
+                    ]
+                }
+            ]
+        }
+    ],
     "OutOfBlinkCors": [
         {
             "platforms": [