Use DOMHighResTimeStamp for notification time.

third_party/WebKit/Source/core/dom/IntersectionObservation.cpp

Index: third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp b/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
index a32edd7be70bcdf562207bb7a3100af44988a3d6..c27f950971a1c5ec0c0e1f94dbd0db668b4435e3 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
@@ -122,7 +122,7 @@ bool IntersectionObservation::computeGeometry(IntersectionGeometry& geometry)
     return true;
 }
 
-void IntersectionObservation::computeIntersectionObservations(double timestamp)
+void IntersectionObservation::computeIntersectionObservations(DOMHighResTimeStamp timestamp)
 {
     // Pre-oilpan, there will be a delay between the time when the target Element gets deleted
     // (because its ref count dropped to zero) and when this IntersectionObservation gets
@@ -149,7 +149,7 @@ void IntersectionObservation::computeIntersectionObservations(double timestamp)
     unsigned newThresholdIndex = observer().firstThresholdGreaterThan(newVisibleRatio);
     if (m_lastThresholdIndex != newThresholdIndex) {
         IntersectionObserverEntry* newEntry = new IntersectionObserverEntry(
-            timestamp / 1000.0,
+            timestamp,

[ojan, 2016/01/22 19:24:10]

I think you need to change IntersectionObserverEntry to store a
DOMHighResTimeStamp as well?

[szager1, 2016/02/02 18:07:51]

Done.

             pixelSnappedIntRect(geometry.targetRect),
             pixelSnappedIntRect(geometry.rootRect),
             pixelSnappedIntRect(geometry.intersectionRect),