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

third_party/WebKit/Source/core/css/StylePropertySerializer.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Research In Motion Limited. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * 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
  * version 2 of the License, or (at your option) any later version.
@@ skipping 835 matching lines @@
     CSSValueID repeatXValueId = repeatX.getValueID();
     CSSValueID repeatYValueId = repeatY.getValueID();
     if (repeatXValueId == repeatYValueId) {
         builder.append(repeatX.cssText());
     } else if (repeatXValueId == CSSValueNoRepeat && repeatYValueId == CSSValueRepeat) {
         builder.append("repeat-y");
     } else if (repeatXValueId == CSSValueRepeat && repeatYValueId == CSSValueNoRepeat) {
         builder.append("repeat-x");
     } else {
         builder.append(repeatX.cssText());
-        builder.append(" ");
+        builder.append(' ');
         builder.append(repeatY.cssText());
     }
 }
 
 String StylePropertySerializer::backgroundRepeatPropertyValue() const
 {
     const CSSValue& repeatX = *m_propertySet.getPropertyCSSValue(CSSPropertyBackgroundRepeatX);
     const CSSValue& repeatY = *m_propertySet.getPropertyCSSValue(CSSPropertyBackgroundRepeatY);
 
     const CSSValueList* repeatXList = 0;
@@ skipping 21 matching lines @@
             builder.append(", ");
 
         const CSSValue& xValue = repeatXList ? repeatXList->item(i % repeatXList->length()) : repeatX;
         const CSSValue& yValue = repeatYList ? repeatYList->item(i % repeatYList->length()) : repeatY;
         appendBackgroundRepeatValue(builder, xValue, yValue);
     }
     return builder.toString();
 }
 
 } // namespace blink