[Passwords] Add Field Trial Testing Config for Touch To Fill

This change adds a field trial testing config for the Touch To Fill
feature on Android.

Bug: 957532
Change-Id: I633e978f4eb4c7c25a5a0c1ee9cf5e0812cc287f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879266Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710227}

testing/variations/fieldtrial_testing_config.json

@@ -538,6 +538,21 @@
             ]
         }
     ],
+    "AndroidTouchToFill": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "TouchToFillAndroid"
+                    ]
+                }
+            ]
+        }
+    ],
     "AppLauncherRefresh": [
         {
             "platforms": [