Revert of Use Document, rather than document element, for implicit root.

third_party/WebKit/Source/core/dom/IntersectionObservation.h

Index: third_party/WebKit/Source/core/dom/IntersectionObservation.h
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObservation.h b/third_party/WebKit/Source/core/dom/IntersectionObservation.h
index 702882a74411ef3e1cf1163e0f82985a87d8314a..e832c6213f2c2bae809479537a4c3a587e07aaff 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObservation.h
+++ b/third_party/WebKit/Source/core/dom/IntersectionObservation.h
@@ -12,7 +12,6 @@
 
 class Element;
 class IntersectionObserver;
-class Node;
 
 class IntersectionObservation : public GarbageCollectedFinalized<IntersectionObservation> {
 public:
@@ -25,7 +24,7 @@
     };
 
     IntersectionObserver& observer() const { return *m_observer; }
-    Element* target() const;
+    Element* target() const { return m_target.get(); }
     bool isActive() const { return m_active; }
     void setActive(bool active) { m_active = active; }
     unsigned lastThresholdIndex() const { return m_lastThresholdIndex; }
@@ -44,12 +43,7 @@
     bool computeGeometry(IntersectionGeometry&);
 
     Member<IntersectionObserver> m_observer;
-
-    // TODO(szager): Why Node instead of Element?  Because NodeIntersectionObserverData::createWeakPtr()
-    // returns a WeakPtr<Node>, which cannot be coerced into a WeakPtr<Element>.  When oilpan rolls out,
-    // this can be changed to WeakMember<Element>.
-    WeakPtrWillBeWeakMember<Node> m_target;
-
+    WeakPtrWillBeWeakMember<Element> m_target;
     unsigned m_active : 1;
     unsigned m_shouldReportRootBounds : 1;
     unsigned m_lastThresholdIndex : 30;