Add Enabled_AutoFetch experiment

Bug: 883486
Change-Id: Ic698365fead980646255f6026a393af7a374b11c
Reviewed-on: https://chromium-review.googlesource.com/c/1454805Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Dan H <harringtond@google.com>
Cr-Commit-Position: refs/heads/master@{#629583}

testing/variations/fieldtrial_testing_config.json

@@ -2932,6 +2932,18 @@
                     },
                     "enable_features": [
                         "NewNetErrorPageUI"
+                    ],
+                    "disable_features": [
+                        "AutoFetchOnNetErrorPage"
+                    ]
+                },
+                {
+                    "name": "Enabled_AutoFetch",
+                    "enable_features": [
+                        "AutoFetchOnNetErrorPage"
+                    ],
+                    "disable_features": [
+                        "NewNetErrorPageUI"
                     ]
                 }
             ]