Use the single char overload of append() when possible.

third_party/WebKit/Source/core/xmlhttprequest/XMLHttpRequest.cpp

 /*
  *  Copyright (C) 2004, 2006, 2008 Apple Inc. All rights reserved.
  *  Copyright (C) 2005-2007 Alexey Proskuryakov <ap@webkit.org>
  *  Copyright (C) 2007, 2008 Julien Chaffraix <jchaffraix@webkit.org>
  *  Copyright (C) 2008, 2011 Google Inc. All rights reserved.
  *  Copyright (C) 2012 Intel Corporation
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
@@ skipping 819 matching lines @@
 void XMLHttpRequest::throwForLoadFailureIfNeeded(ExceptionState& exceptionState, const String& reason)
 {
     if (m_error && !m_exceptionCode)
         m_exceptionCode = NetworkError;
 
     if (!m_exceptionCode)
         return;
 
     String message = "Failed to load '" + m_url.elidedString() + "'";
     if (reason.isNull()) {
-        message.append(".");
+        message.append('.');
     } else {
         message.append(": ");
         message.append(reason);
     }
 
     exceptionState.throwDOMException(m_exceptionCode, message);
 }
 
 void XMLHttpRequest::createRequest(PassRefPtr<EncodedFormData> httpBody, ExceptionState& exceptionState)
 {
@@ skipping 859 matching lines @@
     visitor->trace(m_responseArrayBuffer);
     visitor->trace(m_progressEventThrottle);
     visitor->trace(m_upload);
     visitor->trace(m_blobLoader);
     XMLHttpRequestEventTarget::trace(visitor);
     DocumentParserClient::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
 } // namespace blink