Remove 'String::append' from some of the blink source.

Source/core/fetch/XSLStyleSheetResource.cpp

Index: Source/core/fetch/XSLStyleSheetResource.cpp
diff --git a/Source/core/fetch/XSLStyleSheetResource.cpp b/Source/core/fetch/XSLStyleSheetResource.cpp
old mode 100644
new mode 100755
index 053a445d456640d44516c275622671d2a230703c..76b28b75cd16845ace55cd54a52557f5663d62e4
--- a/Source/core/fetch/XSLStyleSheetResource.cpp
+++ b/Source/core/fetch/XSLStyleSheetResource.cpp
@@ -70,7 +70,7 @@ void XSLStyleSheetResource::checkNotify()
 {
     if (m_data.get()) {
         m_sheet = m_decoder->decode(m_data->data(), encodedSize());
-        m_sheet.append(m_decoder->flush());
+        m_sheet = m_sheet + m_decoder->flush();
     }
 
     ResourceClientWalker<StyleSheetResourceClient> w(m_clients);