Add back field trial config for UnidoOnSignInV2

- Introduced new SharingPreferVapid flag in the tiral

Bug: 1044607
Change-Id: I0ee1c7109593db923146ea8c8ca317d20fd9f894
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2198966Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Alex Chau <alexchau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#768718}

testing/variations/fieldtrial_testing_config.json

@@ -6251,6 +6251,24 @@
             ]
         }
     ],
+    "UnidoOnSignInV2": [
+        {
+            "platforms": [
+                "android",
+                "android_weblayer"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled_2020-05-13",
+                    "enable_features": [
+                        "SharingPreferVapid",
+                        "SharingSendViaSync",
+                        "SyncDeviceInfoInTransportMode"
+                    ]
+                }
+            ]
+        }
+    ],
     "UnifiedAutoplay": [
         {
             "platforms": [