Get rid of obsolete FrameView::m_shouldUpdateViewportIntersection.

third_party/WebKit/Source/core/dom/IntersectionObserver.cpp

Index: third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp b/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
index eade5171943781f148713d6be880359e56c06682..838f8cf59f95e7ccbfe92a3858f9c4a7c4971ad0 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
@@ -220,17 +220,12 @@ bool IntersectionObserver::rootIsValid() const {
 }
 
 Document& IntersectionObserver::trackingDocument() const {
-  Document* document = nullptr;
   if (rootIsImplicit()) {
     DCHECK(m_callback->getExecutionContext());
-    document = toDocument(m_callback->getExecutionContext());
-  } else {
-    DCHECK(root());
-    document = &root()->document();
+    return *toDocument(m_callback->getExecutionContext());
   }
-  DCHECK(document);
-  DCHECK(document->frame());
-  return *document->frame()->localFrameRoot()->document();
+  DCHECK(root());
+  return root()->document();
 }
 
 void IntersectionObserver::observe(Element* target,