Add some important comments around the CrashExitCode tests.

BUG=None

Change-Id: I694f9560b119171d2fd51cde9cd84fab61f2e910
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1813398Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Will Harris <wfh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700893}

chrome/browser/metrics/metrics_service_browsertest.cc

@@ -186,6 +186,8 @@ IN_PROC_BROWSER_TEST_F(MetricsServiceBrowserTest, MAYBE_CrashRenderers) {
   EXPECT_EQ(1, prefs->GetInteger(metrics::prefs::kStabilityRendererCrashCount));
 
 #if defined(OS_WIN)
+  // Consult Stability Team before changing this test as it's recorded to
+  // histograms and used for stability measurement.
   histogram_tester.ExpectUniqueSample(
       "CrashExitCodes.Renderer",
       std::abs(static_cast<int32_t>(STATUS_ACCESS_VIOLATION)), 1);
@@ -230,6 +232,8 @@ IN_PROC_BROWSER_TEST_F(MetricsServiceBrowserTest, MAYBE_CheckCrashRenderers) {
   EXPECT_EQ(1, prefs->GetInteger(metrics::prefs::kStabilityRendererCrashCount));
 
 #if defined(OS_WIN)
+  // Consult Stability Team before changing this test as it's recorded to
+  // histograms and used for stability measurement.
   histogram_tester.ExpectUniqueSample(
       "CrashExitCodes.Renderer",
       std::abs(static_cast<int32_t>(STATUS_BREAKPOINT)), 1);