Add personal info experiment to field trial config.

This is required as we want to rollout finch experiment to beta.

Bug: 1042084
Change-Id: I7921f0434192f51b6942e13fc2307badf3c21c07
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2359789
Commit-Queue: Jing Wang <jiwan@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799449}

testing/variations/fieldtrial_testing_config.json

@@ -142,6 +142,21 @@
             ]
         }
     ],
+    "AssistPersonalInfo": [
+        {
+            "platforms": [
+                "chromeos"
+            ],
+            "experiments": [
+                {
+                    "name": "AssistPersonalInfo",
+                    "enable_features": [
+                        "AssistPersonalInfo"
+                    ]
+                }
+            ]
+        }
+    ],
     "AsyncDns": [
         {
             "platforms": [