IntersectionObserver: Always send an initial notification.

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 2d55282406f2ccc17586036c1e09d555105236ff..5cf0e3411041a753dcc129354c79ae9949837122 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
@@ -63,6 +63,11 @@ void IntersectionObservation::computeIntersectionObservations(
     newVisibleRatio = 0;
     newThresholdIndex = 0;
   }
+
+  // See HACK warning in IntersectionObservation.h
+  newThresholdIndex++;
+  RELEASE_ASSERT(newThresholdIndex < kMaxThresholdIndex);
+
   if (m_lastThresholdIndex != newThresholdIndex) {
     IntRect snappedRootBounds = geometry.rootIntRect();
     IntRect* rootBoundsPointer =