Enable ForegroundVideoCaptureService in fieldtrial_testing_config.json.

This enables foregrounding the video capture service in testing config,
in preparation for experimenting on Beta. This is a performance
optimization which does not change functionality.

Bug: 1066137
Change-Id: If48edced330986353af400cd83144dc9b64ab2f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2210625Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770732}

testing/variations/fieldtrial_testing_config.json

@@ -2396,6 +2396,28 @@
             ]
         }
     ],
+    "ForegroundVideoCaptureService": [
+        {
+            "platforms": [
+                "android",
+                "android_weblayer",
+                "android_webview",
+                "chromeos",
+                "ios",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "ForegroundVideoCaptureService"
+                    ]
+                }
+            ]
+        }
+    ],
     "FormControlsRefresh": [
         {
             "platforms": [