Enable a field trial testing config.

This is required to promote our finch study to Beta and Stable (once
stable finishes releasing that is). We don't expect any noticeable
performance impact.

Bug: 980536
Change-Id: I7913529a00b12c2213c42d2785f5feaf3107372e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1793092
Auto-Submit: Stephen Nusko <nuskos@chromium.org>
Commit-Queue: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695272}

testing/variations/fieldtrial_testing_config.json

@@ -501,6 +501,22 @@
             ]
         }
     ],
+    "AndroidSystemTracing": [
+        {
+            "platforms": [
+                "android",
+                "android_webview"
+            ],
+            "experiments": [
+                {
+                    "name": "EnablePerfettoSystemTracing",
+                    "enable_features": [
+                        "EnablePerfettoSystemTracing"
+                    ]
+                }
+            ]
+        }
+    ],
     "AppLauncherRefresh": [
         {
             "platforms": [