Optional <TimeDelta> since they may be non existent.

chrome/browser/page_load_metrics/observers/from_gws_page_load_metrics_observer_unittest.cc

Index: chrome/browser/page_load_metrics/observers/from_gws_page_load_metrics_observer_unittest.cc
diff --git a/chrome/browser/page_load_metrics/observers/from_gws_page_load_metrics_observer_unittest.cc b/chrome/browser/page_load_metrics/observers/from_gws_page_load_metrics_observer_unittest.cc
index f8bcb254a53fb7a285715348a25bd80202370dd2..d8cb11170edc491882e9ea597d9e601e4f775e66 100644
--- a/chrome/browser/page_load_metrics/observers/from_gws_page_load_metrics_observer_unittest.cc
+++ b/chrome/browser/page_load_metrics/observers/from_gws_page_load_metrics_observer_unittest.cc
@@ -7,6 +7,7 @@
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "chrome/browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.h"
+#include "components/page_load_metrics/browser/page_load_metrics_util.h"
 
 namespace {
 const char kExampleUrl[] = "http://www.example.com/";
@@ -427,16 +428,25 @@ TEST_F(FromGWSPageLoadMetricsObserverTest,
   NavigateAndCommit(GURL("https://www.google.com/search#q=test"));
   NavigateAndCommit(GURL(kExampleUrl));
 
-  SimulateTimingUpdate(timing);
   web_contents()->WasHidden();
+  SimulateTimingUpdate(timing);
 
-  // Navigate again to force logging.
-  NavigateAndCommit(GURL("https://www.final.com"));
-  histogram_tester().ExpectTotalCount(internal::kHistogramFromGWSFirstTextPaint,
-                                      1);
-  histogram_tester().ExpectBucketCount(
-      internal::kHistogramFromGWSFirstTextPaint,
-      timing.first_text_paint.InMilliseconds(), 1);
+  page_load_metrics::PageLoadExtraInfo info =
+      GetPageLoadExtraInfoForCommittedLoad();
+
+  // If the system clock is low resolution PageLoadTracker's background_time_
+  // may be < timing.first_text_paint.
+  if (page_load_metrics::WasStartedInForegroundEventInForeground(
+          timing.first_text_paint, info)) {
+    histogram_tester().ExpectTotalCount(
+        internal::kHistogramFromGWSFirstTextPaint, 1);
+    histogram_tester().ExpectBucketCount(
+        internal::kHistogramFromGWSFirstTextPaint,
+        timing.first_text_paint.InMilliseconds(), 1);
+  } else {
+    histogram_tester().ExpectTotalCount(
+        internal::kHistogramFromGWSFirstTextPaint, 0);
+  }
 }
 
 TEST_F(FromGWSPageLoadMetricsObserverTest, UnknownNavigationBeforeCommit) {
@@ -599,9 +609,20 @@ TEST_F(FromGWSPageLoadMetricsObserverTest, NoAbortNewNavigationAfterPaint) {
   PopulateRequiredTimingFields(&timing);
   NavigateAndCommit(GURL("https://example.test"));
   SimulateTimingUpdate(timing);
+
+  // The test cannot assume that abort time will be > first_paint
+  // (1 micro-sec). If the system clock is low resolution, PageLoadTracker's
+  // abort time may be <= first_paint. In that case the histogram will be
+  // logged. Thus both 0 and 1 counts of histograms are considered good.
+
   NavigateAndCommit(GURL("https://example.test2"));
-  histogram_tester().ExpectTotalCount(
-      internal::kHistogramFromGWSAbortNewNavigationBeforePaint, 0);
+
+  base::HistogramTester::CountsMap counts_map =
+      histogram_tester().GetTotalCountsForPrefix(
+          internal::kHistogramFromGWSAbortNewNavigationBeforePaint);
+
+  EXPECT_TRUE(counts_map.empty() ||
+              (counts_map.size() == 1 && counts_map.begin()->second == 1));
 }
 
 TEST_F(FromGWSPageLoadMetricsObserverTest, NewNavigationBeforeInteraction) {