Accurately update Document node counts on disposing shadow roots.

When cleaning out a ShadowRoot's child Nodes as part of its disposal,
the child Nodes will in some cases not have other references than the
shadow root. If so, the Node will be summarily deleted without being
notified of it being removed from its DOM tree first. By calling its
removedFrom().

As a Document need to maintain an accurate attached node count, arrange
for the otherwise-unreferenced Node's document to be decremented.

R=
BUG=521520

Review URL: https://codereview.chromium.org/1309083002

git-svn-id: svn://svn.chromium.org/blink/trunk@201044 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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

@@ -513,6 +513,9 @@ void ContainerNode::addChildNodesToDeletionQueue(Node*& head, Node*& tail, Conta
             next->setPreviousSibling(nullptr);
 
         if (!n->refCount()) {
+            if (n->inDocument())
+                container.document().decrementNodeCount();
+
 #if ENABLE(SECURITY_ASSERT)
             n->m_deletionHasBegun = true;
 #endif

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

@@ -596,7 +596,6 @@ void Document::dispose()
     DocumentLifecycleNotifier::notifyDocumentWasDisposed();
 
     m_canvasFontCache.clear();
-    m_nodeCount = 0;
 }
 #endif