[Metrics] Add comment about disabled test

Add comment explaining that test is disabled due to flaky failures.

Bug: 1144651
Change-Id: I6ec2f1e100ae833b1ef4324058144204d196ce67
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2527775
Auto-Submit: Toby Huang <tobyhuang@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825838}

chrome/browser/metrics/family_user_metrics_provider_browsertest.cc

@@ -117,6 +117,7 @@ class FamilyUserMetricsProviderTest
   base::test::ScopedFeatureList scoped_feature_list_;
 };
 
+// TODO(crbug/1144651): Test disabled due to flaky failures.
 IN_PROC_BROWSER_TEST_P(FamilyUserMetricsProviderTest, DISABLED_UserCategory) {
   base::HistogramTester histogram_tester;
   // Simulate calling ProvideCurrentSessionData() prior to logging in.