Increase win10_chromium_x64_rel_ng CQ experiment (20% -> 40%)

Bug: 756270
Change-Id: I7cc1dca169c2114a1f76f406134c54f34926d999
Reviewed-on: https://chromium-review.googlesource.com/699837
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506551}

infra/config/cq.cfg

@@ -102,7 +102,7 @@ verifiers {
       builders { name: "win_clang" }
       builders {
         name: "win10_chromium_x64_rel_ng"
-        experiment_percentage: 20
+        experiment_percentage: 40
       }
     }
   }