Replace nextSiblingChildren() with simpler nextSibling() when equivalent

This makes the code more readable as it makes it clear we are only traversing
children. This is also a bit more efficient as nextSiblingChildren() tries to
traverse the ancestors siblings when done with the current siblings.

R=esprehn, adamk

Review URL: https://codereview.chromium.org/196823006

git-svn-id: svn://svn.chromium.org/blink/trunk@169614 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/html/HTMLCollection.cpp

@@ -309,17 +309,17 @@ static inline bool nameShouldBeVisibleInDocumentAll(const HTMLElement& element)
 
 inline Element* firstMatchingChildElement(const HTMLCollection& nodeList, const ContainerNode& root)
 {
-    Element* element = ElementTraversal::firstWithin(root);
+    Element* element = ElementTraversal::firstChild(root);
     while (element && !isMatchingElement(nodeList, *element))
-        element = ElementTraversal::nextSkippingChildren(*element, &root);
+        element = ElementTraversal::nextSibling(*element);
     return element;
 }
 
-inline Element* nextMatchingChildElement(const HTMLCollection& nodeList, Element& current, const ContainerNode& root)
+inline Element* nextMatchingChildElement(const HTMLCollection& nodeList, Element& current)
 {
     Element* next = &current;
     do {
-        next = ElementTraversal::nextSkippingChildren(*next, &root);
+        next = ElementTraversal::nextSibling(*next);
     } while (next && !isMatchingElement(nodeList, *next));
     return next;
 }
@@ -345,7 +345,7 @@ inline Element* HTMLCollection::traverseNextElement(Element& previous, const Con
     if (overridesItemAfter())
         return virtualItemAfter(&previous);
     if (shouldOnlyIncludeDirectChildren())
-        return nextMatchingChildElement(*this, previous, root);
+        return nextMatchingChildElement(*this, previous);
     return nextMatchingElement(*this, previous, root);
 }
 
@@ -368,7 +368,7 @@ Element* HTMLCollection::traverseForwardToOffset(unsigned offset, Element& curre
         }
         if (shouldOnlyIncludeDirectChildren()) {
             Element* next = &currentElement;
-            while ((next = nextMatchingChildElement(*this, *next, root))) {
+            while ((next = nextMatchingChildElement(*this, *next))) {
                 if (++currentOffset == offset)
                     return next;
             }

third_party/WebKit/Source/core/html/HTMLObjectElement.cpp

@@ -440,7 +440,7 @@ bool HTMLObjectElement::containsJavaApplet() const
     if (MIMETypeRegistry::isJavaAppletMIMEType(getAttribute(typeAttr)))
         return true;
 
-    for (HTMLElement* child = Traversal<HTMLElement>::firstWithin(*this); child; child = Traversal<HTMLElement>::nextSkippingChildren(*child, this)) {
+    for (HTMLElement* child = Traversal<HTMLElement>::firstChild(*this); child; child = Traversal<HTMLElement>::nextSibling(*child)) {
         if (isHTMLParamElement(*child)
                 && equalIgnoringCase(child->getNameAttribute(), "type")
                 && MIMETypeRegistry::isJavaAppletMIMEType(child->getAttribute(valueAttr).string()))