Increase win10_chromium_x64_rel_ng experiment to 20%

Bug: 756270
Change-Id: Ica1ab2cf9c8e57dadfb1693b9beae96f3e2240ae
Reviewed-on: https://chromium-review.googlesource.com/677857Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503604}

infra/config/cq.cfg

@@ -108,7 +108,7 @@ verifiers {
       }
       builders {
         name: "win10_chromium_x64_rel_ng"
-        experiment_percentage: 10
+        experiment_percentage: 20
       }
     }
   }