Increase the priority of the chromium_presubmit builder.

The CQ for infra/config changes often only run the chromium_presubmit
builder and when there are outages that affect the builders that share
machines with chromium_presubmit, it means that changes to attempt to
address the outage may experience long pending times and/or require
skipping the presubmit. Increasing the priority will allow us to keep
the safety provided by the presubmit while still being able to land
changes quickly to address outages.

Bug: 1168201
Change-Id: I828ffcf74a162a6ebdaba0075e6d66ffb31ab2c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2643407
Commit-Queue: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845827}

infra/config/generated/cr-buildbucket.cfg

@@ -32636,6 +32636,7 @@ buckets {
         cmd: "recipes"
       }
       properties: "{\"$build/goma\":{\"use_luci_auth\":true},\"$depot_tools/presubmit\":{\"runhooks\":true,\"timeout_s\":480},\"$kitchen\":{\"devshell\":true,\"git_auth\":true},\"$recipe_engine/isolated\":{\"server\":\"https://isolateserver.appspot.com\"},\"builder_group\":\"tryserver.chromium.linux\",\"recipe\":\"presubmit\",\"repo_name\":\"chromium\"}"
+      priority: 25
       execution_timeout_secs: 14400
       expiration_secs: 7200
       caches {

infra/config/subprojects/chromium/try.star

@@ -846,6 +846,11 @@ try_.chromium_linux_builder(
     executable = "recipe:presubmit",
     goma_backend = None,
     main_list_view = "try",
+    # Default priority for buildbucket is 30, see
+    # https://chromium.googlesource.com/infra/infra/+/bb68e62b4380ede486f65cd32d9ff3f1bbe288e4/appengine/cr-buildbucket/creation.py#42
+    # This will improve our turnaround time for landing infra/config changes
+    # when addressing outages
+    priority = 25,
     properties = {
         "$depot_tools/presubmit": {
             "runhooks": True,