[IntersectionObserver] Add isIntersecting field.

third_party/WebKit/LayoutTests/intersection-observer/resources/intersection-observer-test-utils.js

 // Here's how waitForNotification works:
 //
 // - myTestFunction0()
 //   - waitForNotification(myTestFunction1)
 //     - requestAnimationFrame()
 //   - Modify DOM in a way that should trigger an IntersectionObserver callback.
 // - BeginFrame
 //   - requestAnimationFrame handler runs
 //     - First setTimeout()
 //   - Style, layout, paint
@@ skipping 68 matching lines @@
   if (expected) {
     checkRect(
         entries[i].boundingClientRect, expected.slice(0, 4),
         'entries[' + i + '].boundingClientRect');
     checkRect(
         entries[i].intersectionRect, expected.slice(4, 8),
         'entries[' + i + '].intersectionRect');
     checkRect(
         entries[i].rootBounds, expected.slice(8, 12),
         'entries[' + i + '].rootBounds');
+    if (expected.length > 12) {
+      assert_equals(
+          entries[i].isIntersecting, expected[12],
+          'entries[' + i + '].isIntersecting');
+    }
   }
 }
 
 function checkJsonEntry(actual, expected) {
   checkRect(
       actual.boundingClientRect, expected.boundingClientRect,
       'entry.boundingClientRect');
   checkRect(
       actual.intersectionRect, expected.intersectionRect,
       'entry.intersectionRect');
   if (actual.rootBounds == 'null')
     assert_equals(expected.rootBounds, 'null', 'rootBounds is null');
   else
     checkRect(actual.rootBounds, expected.rootBounds, 'entry.rootBounds');
   assert_equals(actual.target, expected.target);
 }
 
 function checkJsonEntries(actual, expected, description) {
   test(function() {
     assert_equals(actual.length, expected.length);
     for (var i = 0; i < actual.length; i++)
       checkJsonEntry(actual[i], expected[i]);
   }, description);
 }