Add a fieldtrial testing config for ExtendedShellExtensionsEnumeration

Bug: 889346
Change-Id: I44a357c52c0a37064e1bb98bf2cfaef44e60db6b
Reviewed-on: https://chromium-review.googlesource.com/1246947Reviewed-by: Robert Kaplow (sloooow) <rkaplow@chromium.org>
Commit-Queue: Patrick Monette <pmonette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595196}

testing/variations/fieldtrial_testing_config.json

@@ -1787,6 +1787,21 @@
             ]
         }
     ],
+    "ExtendedShellExtensionsEnumeration": [
+        {
+            "platforms": [
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "ExtendedShellExtensionsEnumeration"
+                    ]
+                }
+            ]
+        }
+    ],
     "ExtensionContentVerification": [
         {
             "platforms": [