Avoid calling slower Node::firstChild() / Node::lastChild() when possible

Source/core/editing/ApplyStyleCommand.h

 /*
  * Copyright (C) 2005, 2006, 2008, 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
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     Position positionToComputeInlineStyleChange(PassRefPtrWillBeRawPtr<Node>, RefPtrWillBeMember<Node>& dummyElement);
     void applyInlineStyleChange(PassRefPtrWillBeRawPtr<Node> startNode, PassRefPtrWillBeRawPtr<Node> endNode, StyleChange&, EAddStyledElement);
     void splitTextAtStart(const Position& start, const Position& end);
     void splitTextAtEnd(const Position& start, const Position& end);
     void splitTextElementAtStart(const Position& start, const Position& end);
     void splitTextElementAtEnd(const Position& start, const Position& end);
     bool shouldSplitTextElement(Element*, EditingStyle*);
     bool isValidCaretPositionInTextNode(const Position& position);
     bool mergeStartWithPreviousIfIdentical(const Position& start, const Position& end);
     bool mergeEndWithNextIfIdentical(const Position& start, const Position& end);
-    void cleanupUnstyledAppleStyleSpans(Node* dummySpanAncestor);
+    void cleanupUnstyledAppleStyleSpans(ContainerNode* dummySpanAncestor);
 
     void surroundNodeRangeWithElement(PassRefPtrWillBeRawPtr<Node> start, PassRefPtrWillBeRawPtr<Node> end, PassRefPtrWillBeRawPtr<Element>);
     float computedFontSize(Node*);
-    void joinChildTextNodes(Node*, const Position& start, const Position& end);
+    void joinChildTextNodes(ContainerNode*, const Position& start, const Position& end);
 
     HTMLElement* splitAncestorsWithUnicodeBidi(Node*, bool before, WritingDirection allowedDirection);
     void removeEmbeddingUpToEnclosingBlock(Node* node, Node* unsplitAncestor);
 
     void updateStartEnd(const Position& newStart, const Position& newEnd);
     Position startPosition();
     Position endPosition();
 
     RefPtrWillBeMember<EditingStyle> m_style;
     EditAction m_editingAction;
     EPropertyLevel m_propertyLevel;
     Position m_start;
     Position m_end;
     bool m_useEndingSelection;
     RefPtrWillBeMember<Element> m_styledInlineElement;
     bool m_removeOnly;
     IsInlineElementToRemoveFunction m_isInlineElementToRemoveFunction;
 };
 
 enum ShouldStyleAttributeBeEmpty { AllowNonEmptyStyleAttribute, StyleAttributeShouldBeEmpty };
 bool isEmptyFontTag(const Element*, ShouldStyleAttributeBeEmpty = StyleAttributeShouldBeEmpty);
 bool isLegacyAppleStyleSpan(const Node*);
 bool isStyleSpanOrSpanWithOnlyStyleAttribute(const Element*);
 PassRefPtrWillBeRawPtr<HTMLElement> createStyleSpanElement(Document&);
 
 } // namespace WebCore
 
 #endif