[base] Disable flaky HangWatcherRealTimeTest.

The HangWatcherRealTimeTest.PeriodicCallsCount test assumes timely
execution of tasks and therefore flakes when run in slow/variable
environments such as ASAN or nested virtualization.

Disable the test until it can be made robust against this.

TBR=olivierli

Bug: 1064116
Change-Id: I080841124b44571616888b24f808c6608cf5906f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2118052Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#752824}

base/threading/hang_watcher_unittest.cc

@@ -226,7 +226,9 @@ class HangWatcherRealTimeTest : public testing::Test {
   base::ScopedClosureRunner unregister_thread_closure_;
 };
 
-TEST_F(HangWatcherRealTimeTest, PeriodicCallsCount) {
+// TODO(https://crbug.com/1064116): Fix this test not to rely on timely task
+// execution, which results in flakiness on slower bots.
+TEST_F(HangWatcherRealTimeTest, DISABLED_PeriodicCallsCount) {
   // These values are chosen to execute fast enough while running the unit tests
   // but be large enough to buffer against clock precision problems.
   const base::TimeDelta kMonitoringPeriod(