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

Source/core/inspector/InspectorFileSystemAgent.cpp

Index: Source/core/inspector/InspectorFileSystemAgent.cpp
diff --git a/Source/core/inspector/InspectorFileSystemAgent.cpp b/Source/core/inspector/InspectorFileSystemAgent.cpp
index 2d7c793776531a3fb1901f7697ecb299ddf2135d..28fd555cdd534b7cedf044363c26d847b2e30d14 100644
--- a/Source/core/inspector/InspectorFileSystemAgent.cpp
+++ b/Source/core/inspector/InspectorFileSystemAgent.cpp
@@ -491,7 +491,7 @@ void FileContentRequest::didRead()
 
     OwnPtr<TextResourceDecoder> decoder = TextResourceDecoder::create(m_mimeType, m_charset, true);
     String result = decoder->decode(static_cast<char*>(buffer->data()), buffer->byteLength());
-    result.append(decoder->flush());
+    result = result + decoder->flush();
     m_charset = decoder->encoding().name();
     reportResult(static_cast<FileError::ErrorCode>(0), &result, &m_charset);
 }