Make TreeScope::documentScope() return a reference and ensure m_documentScope is never NULL

Source/core/dom/TreeScopeAdopter.cpp

Index: Source/core/dom/TreeScopeAdopter.cpp
diff --git a/Source/core/dom/TreeScopeAdopter.cpp b/Source/core/dom/TreeScopeAdopter.cpp
index 366b4af3fa15f793b06ee6ab9733cfd114fc46f2..d3832629729a537c7eab041b0b7f34d8fb9c74f9 100644
--- a/Source/core/dom/TreeScopeAdopter.cpp
+++ b/Source/core/dom/TreeScopeAdopter.cpp
@@ -44,18 +44,17 @@ void TreeScopeAdopter::moveTreeToNewScope(Node& root) const
     // that element may contain stale data as changes made to it will have updated the DOMTreeVersion
     // of the document it was moved to. By increasing the DOMTreeVersion of the donating document here
     // we ensure that the collection cache will be invalidated as needed when the element is moved back.
-    Document* oldDocument = m_oldScope.documentScope();
-    ASSERT(oldDocument);
-    Document* newDocument = m_newScope.documentScope();
+    Document& oldDocument = m_oldScope.documentScope();
+    Document& newDocument = m_newScope.documentScope();
     bool willMoveToNewDocument = oldDocument != newDocument;
     if (willMoveToNewDocument)
-        oldDocument->incDOMTreeVersion();
+        oldDocument.incDOMTreeVersion();
 
     for (Node* node = &root; node; node = NodeTraversal::next(*node, &root)) {
         updateTreeScope(*node);
 
         if (willMoveToNewDocument)
-            moveNodeToNewDocument(*node, *oldDocument, newDocument);
+            moveNodeToNewDocument(*node, oldDocument, newDocument);
         else if (node->hasRareData()) {
             NodeRareData* rareData = node->rareData();
             if (rareData->nodeLists())
@@ -74,14 +73,14 @@ void TreeScopeAdopter::moveTreeToNewScope(Node& root) const
         for (ShadowRoot* shadow = node->youngestShadowRoot(); shadow; shadow = shadow->olderShadowRoot()) {
             shadow->setParentTreeScope(&m_newScope);
             if (willMoveToNewDocument)
-                moveTreeToNewDocument(*shadow, *oldDocument, newDocument);
+                moveTreeToNewDocument(*shadow, oldDocument, newDocument);
         }
     }
 
     m_oldScope.guardDeref();
 }
 
-void TreeScopeAdopter::moveTreeToNewDocument(Node& root, Document& oldDocument, Document* newDocument) const
+void TreeScopeAdopter::moveTreeToNewDocument(Node& root, Document& oldDocument, Document& newDocument) const
 {
     for (Node* node = &root; node; node = NodeTraversal::next(*node, &root)) {
         moveNodeToNewDocument(*node, oldDocument, newDocument);
@@ -111,17 +110,17 @@ inline void TreeScopeAdopter::updateTreeScope(Node& node) const
     node.setTreeScope(&m_newScope);
 }
 
-inline void TreeScopeAdopter::moveNodeToNewDocument(Node& node, Document& oldDocument, Document* newDocument) const
+inline void TreeScopeAdopter::moveNodeToNewDocument(Node& node, Document& oldDocument, Document& newDocument) const
 {
     ASSERT(!node.inDocument() || oldDocument != newDocument);
 
     if (node.hasRareData()) {
         NodeRareData* rareData = node.rareData();
         if (rareData->nodeLists())
-            rareData->nodeLists()->adoptDocument(&oldDocument, newDocument);
+            rareData->nodeLists()->adoptDocument(oldDocument, newDocument);
     }
 
-    oldDocument.moveNodeIteratorsToNewDocument(&node, newDocument);
+    oldDocument.moveNodeIteratorsToNewDocument(node, newDocument);
 
     if (node.isShadowRoot())
         toShadowRoot(node).setDocumentScope(newDocument);