[Autofill] Added UseImprovedLabelDisambiguation to testing file.

Bug: 953073
Change-Id: Ib0ffe69b177ddbbe2694fe701de791e5779dab60
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1566596
Auto-Submit: Caitlin Fischer <caitlinfischer@google.com>
Reviewed-by: Tommy Martino <tmartino@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652271}

testing/variations/fieldtrial_testing_config.json

@@ -1064,6 +1064,24 @@
             ]
         }
     ],
+    "AutofillUseImprovedLabelDisambiguation": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "AutofillUseImprovedLabelDisambiguation"
+                    ]
+                }
+            ]
+        }
+    ],
     "AutomaticTabDiscarding": [
         {
             "platforms": [