IntersectionObserver: check threshold parameters for NaN.

third_party/WebKit/LayoutTests/intersection-observer/observer-exceptions.html

Index: third_party/WebKit/LayoutTests/intersection-observer/observer-exceptions.html
diff --git a/third_party/WebKit/LayoutTests/intersection-observer/observer-exceptions.html b/third_party/WebKit/LayoutTests/intersection-observer/observer-exceptions.html
index 03a6c2ba3c979e066be82c5455f8a086fa247d2e..a266655239ff77d0c76910f2633f965edd49d8c6 100644
--- a/third_party/WebKit/LayoutTests/intersection-observer/observer-exceptions.html
+++ b/third_party/WebKit/LayoutTests/intersection-observer/observer-exceptions.html
@@ -16,6 +16,14 @@
   }
 
   try {
+    new IntersectionObserver(e => {}, {threshold: ["foo"]});
+    testFailed("IntersectionObserver constructor did not throw due to invalid threshold.");
+  } catch(e) {
+    exc = e;
+    shouldBeType("exc", "RangeError");
+  }
+
+  try {
     new IntersectionObserver(e => {}, {rootMargin: "1"});
     testFailed("IntersectionObserver constructor did not throw due to invalid rootMargin.");
   } catch(e) {