IntersectionObserver: compute correct intersection ratio for 0x0 elements

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 2ae1556fc10ddca7a031867902c3f74dde19c9c3..40edeb5ac586fcb50fdb3dd10c16b5757d3d0508 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
@@ -53,6 +53,7 @@ void IntersectionObservation::computeIntersectionObservations(
   float newVisibleRatio = 0;
   if (geometry.targetRect().isEmpty()) {
     newThresholdIndex = geometry.doesIntersect() ? 1 : 0;
+    newVisibleRatio = geometry.doesIntersect() ? 1 : 0;

[szager1, 2016/12/09 17:30:07]

You also need to delete the preceding line, and instead use the same logic as
for the non-degenerate case to get newThresholdIndex (i.e.,
observer().firstThresholdGreaterThan(newVisibleRatio)).

[Sami, 2016/12/09 17:51:16]

Good catch. Rewrote this as we discussed offline.

   } else if (!geometry.doesIntersect()) {
     newThresholdIndex = 0;
   } else {