[cq] Add chromium win trybot as experiment

This will be temporarily added to the V8 CQ in a follow up
to prevent win-specific gn breakages. It will be removed
once v8 has its own full gn coverage on windows.

BUG=chromium:474921
NOTRY=true

Review-Url: https://codereview.chromium.org/2144193002
Cr-Commit-Position: refs/heads/master@{#37747}

infra/config/cq.cfg

@@ -107,6 +107,13 @@ verifiers {
         experiment_percentage: 100
       }
     }
+    buckets {
+      name: "master.tryserver.chromium.win"
+      builders {
+        name: "win_chromium_compile_dbg_ng"
+        experiment_percentage: 100
+      }
+    }
   }
 
   sign_cla {}