[cq.cfg] Move chromium_presubmit to 100% on LUCI.

R=jbudorick@chromium.org

Bug: 731553
Change-Id: I064be66068ef0a02e5bab21061112d6174395246
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/893654Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533281}

infra/config/cq.cfg

@@ -78,7 +78,7 @@ verifiers {
       }
       builders {
         name: "chromium_presubmit"
-        equivalent_to { bucket: "luci.chromium.try" percentage: 50 }
+        equivalent_to { bucket: "luci.chromium.try" percentage: 100 }
       }
       builders {
         name: "fuchsia_arm64"