android: Enable ServiceGroupImportance in tests

Note this feature only applies to Android Q, which has no automated
testing coverage right now.

Bug: 946216
Change-Id: I88dcedb0595815c9a2e8384539a249d43196ae02
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1786833
Commit-Queue: Bo <boliu@chromium.org>
Reviewed-by: ssid <ssid@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694957}

testing/variations/fieldtrial_testing_config.json

@@ -5257,6 +5257,21 @@
             ]
         }
     ],
+    "ServiceGroupImportance": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "ServiceGroupImportance"
+                    ]
+                }
+            ]
+        }
+    ],
     "ServiceManagerForBackgroundPrefetch": [
         {
             "platforms": [