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

Source/core/fetch/FontResource.cpp

Index: Source/core/fetch/FontResource.cpp
diff --git a/Source/core/fetch/FontResource.cpp b/Source/core/fetch/FontResource.cpp
old mode 100644
new mode 100755
index 0fdbcc1d39e9a76f602f07f8dc2a14315522a5f4..319a2c0e5f4a3fe3b8e33e4f422cf197b59142c0
--- a/Source/core/fetch/FontResource.cpp
+++ b/Source/core/fetch/FontResource.cpp
@@ -110,10 +110,11 @@ bool FontResource::ensureSVGFontData()
             m_externalSVGDocument = SVGDocument::create();
 
             OwnPtr<TextResourceDecoder> decoder = TextResourceDecoder::create("application/xml");
-            String svgSource = decoder->decode(m_data->data(), m_data->size());
+            StringBuilder svgSource;
+            svgSource.append(decoder->decode(m_data->data(), m_data->size()));
             svgSource.append(decoder->flush());
 
-            m_externalSVGDocument->setContent(svgSource);
+            m_externalSVGDocument->setContent(svgSource.toString());
 
             if (decoder->sawError())
                 m_externalSVGDocument = 0;