Re-enable "chromium.resultdb.result_sink" experiment on chromium ci builders at 10%

Bug: 1108016
Change-Id: I5e63664b302698c805361043113d940432c5907e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485050Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Chan Li <chanli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818628}

infra/config/lib/ci.star

@@ -339,6 +339,7 @@ def ci_builder(
         tree_closing = False,
         notifies = None,
         resultdb_bigquery_exports = None,
+        experiments = None,
         **kwargs):
     """Define a CI builder.
 
@@ -376,6 +377,8 @@ def ci_builder(
         specifying additional parameters for exporting test results to BigQuery.
         Will always upload to the luci-resultdb.chromium.ci_test_results table
         in addition to any tables specified by the list's elements.
+      experiments - a dict of experiment name to the percentage chance (0-100)
+        that it will apply to builds generated from this builder.
     """
     if not branches.matches(branch_selector):
         return
@@ -393,6 +396,10 @@ def ci_builder(
     ]
     merged_resultdb_bigquery_exports.extend(resultdb_bigquery_exports or [])
 
+    # Enable "chromium.resultdb.result_sink" on all ci builders for 10% by default.
+    experiments = experiments or {}
+    experiments.setdefault("chromium.resultdb.result_sink", 10)
+
     # Define the builder first so that any validation of luci.builder arguments
     # (e.g. bucket) occurs before we try to use it
     builders.builder(
@@ -400,6 +407,7 @@ def ci_builder(
         branch_selector = branch_selector,
         resultdb_bigquery_exports = merged_resultdb_bigquery_exports,
         notifies = notifies,
+        experiments = experiments,
         **kwargs
     )