[resultdb] enable resultdb for junit_tests on andriod,clang at 50%

ResultDB for junit_tests was enabled on chromium.android at 30%, and
100% of the builds succeeded with resultdb.
https://screenshot.googleplex.com/BvHH2VDXm7hGvCh

There are only 3 builder groups with junit_tests in chromium.
- chromium.fyi
- chromium.android
- chromium.clang

If all builds on android and clang succeed after this CL, the next CL
will enable ResultDB for junit tests on all builders at 100% rate.
(Dec 14)

R=gbeaty@chromium.org,chanli@chromium.org

Bug: 1084332
Change-Id: Ie8aa34868b58a64e0f88e2099cb6ceef01256af3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587495Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Chan Li <chanli@chromium.org>
Commit-Queue: Scott Lee <ddoman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836313}

infra/config/lib/ci.star

@@ -507,7 +507,7 @@ def android_builder(
         goma_backend = builders.goma.backend.RBE_PROD,
         goma_jobs = goma_jobs,
         experiments = {
-            "chromium.resultdb.result_sink.junit_tests": 30,
+            "chromium.resultdb.result_sink.junit_tests": 50,
         },
         **kwargs
     )
@@ -553,6 +553,9 @@ def clang_builder(*, name, builderless = True, cores = 32, properties = None, **
         # CFI builds will take even longer - around 11h.
         execution_timeout = 14 * time.hour,
         properties = properties,
+        experiments = {
+            "chromium.resultdb.result_sink.junit_tests": 50,
+        },
         **kwargs
     )