Demistify DocumentParser::append

Source/core/xml/parser/XMLDocumentParser.cpp

Index: Source/core/xml/parser/XMLDocumentParser.cpp
diff --git a/Source/core/xml/parser/XMLDocumentParser.cpp b/Source/core/xml/parser/XMLDocumentParser.cpp
index 531e397b7eddf871ba1add52cc4876c270b0355e..e2738240ce8ca06b1d335f98474a90717198049c 100644
--- a/Source/core/xml/parser/XMLDocumentParser.cpp
+++ b/Source/core/xml/parser/XMLDocumentParser.cpp
@@ -347,9 +347,9 @@ void XMLDocumentParser::insert(const SegmentedString&)
     ASSERT_NOT_REACHED();
 }
 
-void XMLDocumentParser::append(PassRefPtr<StringImpl> inputSource)
+void XMLDocumentParser::append(const String& inputSource)
 {
-    SegmentedString source(inputSource);
+    const SegmentedString source(inputSource);
     if (m_sawXSLTransform || !m_sawFirstElement)
         m_originalSourceForTransform.append(source);