Eliminate superfluous clearing of weak pointer.

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/IntersectionObserver.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/css/parser/CSSParserTokenRange.h"
 #include "core/css/parser/CSSTokenizer.h"
 #include "core/dom/ElementIntersectionObserverData.h"
@@ skipping 142 matching lines @@
         observation->computeIntersectionObservations(timestamp);
 }
 
 void IntersectionObserver::disconnect()
 {
     HeapVector<Member<IntersectionObservation>> observationsToDisconnect;
     copyToVector(m_observations, observationsToDisconnect);
     for (auto& observation : observationsToDisconnect)
         observation->disconnect();
     ASSERT(m_observations.isEmpty());
-    m_root.clear();
 }
 
 void IntersectionObserver::removeObservation(IntersectionObservation& observation)
 {
     m_observations.remove(&observation);
 }
 
 HeapVector<Member<IntersectionObserverEntry>> IntersectionObserver::takeRecords()
 {
     checkRootAndDetachIfNeeded();
@@ skipping 54 matching lines @@
 
 DEFINE_TRACE(IntersectionObserver)
 {
     visitor->trace(m_callback);
     visitor->trace(m_root);
     visitor->trace(m_observations);
     visitor->trace(m_entries);
 }
 
 } // namespace blink