Clamp invalidating input time at nav start

In some edge cases (e.g. inaccurate input timestamp provided through
remote debugging protocol) we might receive an input timestamp that is
earlier than navigation start. Since invalidating input timestamp before
navigation start in non-sensical, we clamp it at navigation start.

R=tdresser@chromium.org,japhet@chromium.org

Bug: 797334
Change-Id: Ib12921e5d372b0f676a6182fd3cd643b7e12a5f8
Reviewed-on: https://chromium-review.googlesource.com/895410Reviewed-by: Nate Chapin <japhet@chromium.org>
Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Commit-Queue: Deepanjan Roy <dproy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534126}

third_party/WebKit/Source/core/loader/InteractiveDetector.cpp

@@ -215,7 +215,13 @@ void InteractiveDetector::OnInvalidatingInputEvent(
   if (!page_event_times_.first_invalidating_input.is_null())
     return;
 
-  page_event_times_.first_invalidating_input = invalidation_time;
+  // In some edge cases (e.g. inaccurate input timestamp provided through remote
+  // debugging protocol) we might receive an input timestamp that is earlier
+  // than navigation start. Since invalidating input timestamp before navigation
+  // start in non-sensical, we clamp it at navigation start.
+  page_event_times_.first_invalidating_input =
+      std::max(invalidation_time, page_event_times_.nav_start);
+
   if (GetSupplementable()->Loader())
     GetSupplementable()->Loader()->DidChangePerformanceTiming();
 }

third_party/WebKit/Source/core/loader/InteractiveDetectorTest.cpp

@@ -399,6 +399,23 @@ TEST_F(InteractiveDetectorTest, InvalidatingUserInput) {
             t0 + 5.0);
 }
 
+TEST_F(InteractiveDetectorTest, InvalidatingUserInputClampedAtNavStart) {
+  double t0 = CurrentTimeTicksInSeconds();
+  SimulateNavigationStart(t0);
+  // Network is forever quiet for this test.
+  SetActiveConnections(1);
+  SimulateDOMContentLoadedEnd(t0 + 2.0);
+  SimulateFMPDetected(/* fmp_time */ t0 + 3.0, /* detection_time */ t0 + 4.0);
+  // Invalidating input timestamp is earlier than navigation start.
+  SimulateInteractiveInvalidatingInput(t0 - 10.0);
+  // Run till 5 seconds after long task 2 end.
+  RunTillTimestamp((t0 + 7.1) + 5.0 + 0.1);
+  EXPECT_EQ(GetInteractiveTime(), t0 + 3.0);  // TTI at FMP.
+  // Invalidating input timestamp is clamped at navigation start.
+  EXPECT_EQ(TimeTicksInSeconds(GetDetector()->GetFirstInvalidatingInputTime()),
+            t0);
+}
+
 class InteractiveDetectorTestWithDummyPage : public PageTestBase {
  public:
   // Public because it's executed on a task queue.