Make DisableFirstRunAutoImport default on trunk in view of Stable experiment.

testing/variations/fieldtrial_testing_config.json

 {
     "AndroidSessionNotifications": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "Disabled"
                 }
@@ skipping 454 matching lines @@
             "experiments": [
                 {
                     "name": "DefaultEnableGpuRasterization",
                     "enable_features": [
                         "DefaultEnableGpuRasterization"
                     ]
                 }
             ]
         }
     ],
+    "DisableFirstRunAutoImport": [
+        {
+            "platforms": [
+                "win"
+            ],
+            "experiments": [
+                {
+                    "name": "DisableFirstRunAutoImport",
+                    "enable_features": [
+                        "DisableFirstRunAutoImport"
+                    ]
+                }
+            ]
+        }
+    ],
     "DisallowFetchForDocWrittenScriptsInMainFrame": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "DocumentWriteEvaluatorGroup",
                     "params": {
                         "disallowFetchForDocWrittenScriptsInMainFrame": "false",
@@ skipping 1916 matching lines @@
                 {
                     "name": "Enabled",
                     "enable_features": [
                         "use-new-media-cache"
                     ]
                 }
             ]
         }
     ]
 }