[Autofill] Field study to measure impact of Variations supplied country codes.

Bug: 1065001
Change-Id: If942491a835311080ef5f64f4cce76e3ba64ca67
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2121267Reviewed-by: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Matthias Körber <koerber@google.com>
Commit-Queue: Matthias Körber <koerber@google.com>
Cr-Commit-Position: refs/heads/master@{#756980}

testing/variations/fieldtrial_testing_config.json

@@ -974,6 +974,27 @@
             ]
         }
     ],
+    "AutofillUseVariationCountryCode": [
+        {
+            "platforms": [
+                "android",
+                "android_weblayer",
+                "chromeos",
+                "ios",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "AutofillUseVariationCountryCode"
+                    ]
+                }
+            ]
+        }
+    ],
     "BackForwardCache": [
         {
             "platforms": [