Enable Finch Trial Test for MacV2Sandbox.

Bug: 749839
Change-Id: Ie95fc3c6574377e278474c1709b7270847016b44
Reviewed-on: https://chromium-review.googlesource.com/596422Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Greg Kerr <kerrnel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491576}

testing/variations/fieldtrial_testing_config.json

@@ -1332,6 +1332,21 @@
             ]
         }
     ],
+    "MacV2Sandbox": [
+        {
+            "platforms": [
+                "mac"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "MacV2Sandbox"
+                    ]
+                }
+            ]
+        }
+    ],
     "MaxDelayableRequestsNetworkOverride": [
         {
             "platforms": [