Add fieldtrial config for UMA and UKM Demographics

Bug: 978849, 1006806
Change-Id: Id797a8c9955ece26668490664f07c83756d0f6a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1906335Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Roger McFarlane <rogerm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713963}

testing/variations/fieldtrial_testing_config.json

@@ -6640,6 +6640,27 @@
             ]
         }
     ],
+    "UmaAndUkmDemographics": [
+        {
+            "platforms": [
+                "android",
+                "chromeos",
+                "linux",
+                "mac",
+                "windows",
+                "ios"
+            ],
+            "experiments": [
+                {
+                    "name": "UKM_Enabled",
+                    "enable_features": [
+                        "DemographicMetricsReporting",
+                        "UkmReportNoisedUserBirthYearAndGender"
+                    ]
+                }
+            ]
+        }
+    ],
     "UnifiedAutoplay": [
         {
             "platforms": [