Add finch config for assistive autocorrect

Bug: 1060433
Change-Id: I77cc133461fe5f6336bb843184d387565b8a7d68
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2428266
Auto-Submit: John Palmer <jopalmer@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812302}

testing/variations/fieldtrial_testing_config.json

@@ -514,6 +514,21 @@
             ]
         }
     ],
+    "AssistAutocorrect": [
+        {
+            "platforms": [
+                "chromeos"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled_20200925",
+                    "enable_features": [
+                        "AssistAutocorrect"
+                    ]
+                }
+            ]
+        }
+    ],
     "AssistPersonalInfo": [
         {
             "platforms": [