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

Source/core/fetch/CSSStyleSheetResource.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 71 matching lines @@
     ASSERT(!isPurgeable());
 
     if (!m_data || m_data->isEmpty() || !canUseSheet(enforceMIMEType, hasValidMIMEType))
         return String();
 
     if (!m_decodedSheetText.isNull())
         return m_decodedSheetText;
 
     // Don't cache the decoded text, regenerating is cheap and it can use quite a bit of memory
     String sheetText = m_decoder->decode(m_data->data(), m_data->size());
-    sheetText.append(m_decoder->flush());
+    sheetText = sheetText + m_decoder->flush();
     return sheetText;
 }
 
 void CSSStyleSheetResource::checkNotify()
 {
     // Decode the data to find out the encoding and keep the sheet text around during checkNotify()
     if (m_data) {
         m_decodedSheetText = m_decoder->decode(m_data->data(), m_data->size());
         m_decodedSheetText.append(m_decoder->flush());
     }
@@ skipping 71 matching lines @@
 
     if (m_parsedStyleSheetCache)
         m_parsedStyleSheetCache->removedFromMemoryCache();
     m_parsedStyleSheetCache = sheet;
     m_parsedStyleSheetCache->addedToMemoryCache();
 
     setDecodedSize(m_parsedStyleSheetCache->estimatedSizeInBytes());
 }
 
 }