Speed up message loop perf test and disable failing waitable event perf test

In order to reduce cycle time on the performance waterfall, drop the
perf test measurement period from 30s to 5s.

Bug: 897751, 848499
Change-Id: I3cd921b327044f02767bc8a43a6e99e5a8a6f48f
Reviewed-on: https://chromium-review.googlesource.com/c/1315967Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605922}

base/message_loop/message_loop_task_runner_perftest.cc

@@ -28,8 +28,7 @@ namespace {
 
 // Tests below will post tasks in a loop until |kPostTaskPerfTestDuration| has
 // elapsed.
-constexpr TimeDelta kPostTaskPerfTestDuration =
-    base::TimeDelta::FromSeconds(30);
+constexpr TimeDelta kPostTaskPerfTestDuration = base::TimeDelta::FromSeconds(5);
 
 }  // namespace
 

base/synchronization/waitable_event_perftest.cc

@@ -150,7 +150,8 @@ TEST(WaitableEventPerfTest, MultipleThreads) {
   PrintPerfWaitableEvent(&signaler, "_signaler", "multithread-1000-samples");
 }
 
-TEST(WaitableEventPerfTest, Throughput) {
+// See crbug.com/848499.
+TEST(WaitableEventPerfTest, DISABLED_Throughput) {
   // Reserve a lot of sample space.
   const size_t kCapacity = 500000;
   TraceWaitableEvent event(kCapacity);