Increase minimum tests classes per shard.

Certain suites like ui_junit_tests and base_junit_tests need less
shards, time differences are more apparent on bots than when run
locally.

Bug: 1138506
Change-Id: I5c5cbf019300f9b438c5d23b996e7d326e8e050d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2545570
Auto-Submit: benjamin joyce <bjoyce@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829066}

build/android/pylib/local/machine/local_machine_junit_test_run.py

@@ -48,7 +48,7 @@ _MAX_SHARDS = 10
 # It can actually take longer to run if you shard too much, especially on
 # smaller suites. Locally media_base_junit_tests takes 4.3 sec with 1 shard,
 # and 6 sec with 2 or more shards.
-_MIN_CLASSES_PER_SHARD = 4
+_MIN_CLASSES_PER_SHARD = 8
 
 
 class LocalMachineJunitTestRun(test_run.TestRun):

build/android/pylib/local/machine/local_machine_junit_test_run_test.py

@@ -58,7 +58,7 @@ class LocalMachineJunitTestRunTests(unittest.TestCase):
     self.assertEquals(local_machine_junit_test_run._MAX_SHARDS, shards)
 
     # Tests using min_class per shards.
-    test_classes = [1] * 10
+    test_classes = [1] * 20
     test_shards = 8
     shards = local_machine_junit_test_run.ChooseNumOfShards(
         test_classes, test_shards)