Adjust leak detector expectations for IntersectionObserver

content/shell/renderer/layout_test/leak_detector.cc

Index: content/shell/renderer/layout_test/leak_detector.cc
diff --git a/content/shell/renderer/layout_test/leak_detector.cc b/content/shell/renderer/layout_test/leak_detector.cc
index bc8de7e5449d18443d6618b92c89e1d6b8cd107d..92123cb7bb870ae047ea7caeee7a26858e6fc22e 100644
--- a/content/shell/renderer/layout_test/leak_detector.cc
+++ b/content/shell/renderer/layout_test/leak_detector.cc
@@ -31,8 +31,10 @@ const int kInitialNumberOfLiveFrames = 1;
 const int kInitialNumberOfWorkerGlobalScopes = 0;
 
 // In the initial state, there are two ActiveDOMObjects (FontFaceSet created by
-// HTMLDocument and SuspendableTimer created by DocumentLoader).
-const int kInitialNumberOfLiveActiveDOMObject = 2;
+// HTMLDocument and SuspendableTimer created by DocumentLoader). A third one
+// (IntersectionObserverController) may be created if the root document
+// registers an intersection observer.
+const int kInitialNumberOfLiveActiveDOMObject = 3;
 
 // This includes not only about:blank's context but also ScriptRegexp (e.g.
 // created by isValidEmailAddress in EmailInputType.cpp). The leak detector