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

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

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer.
@@ skipping 307 matching lines @@
         if (!areDefaultCornerRadii) {
             result.append(separator);
             result.append(cornersSeparator);
 
             for (size_t i = 0; i < horizontalRadii.size(); ++i) {
                 result.append(separator);
                 result.append(horizontalRadii[i]);
             }
             if (horizontalRadii != verticalRadii) {
                 result.append(separator);
-                result.append("/");
+                result.append('/');
 
                 for (size_t i = 0; i < verticalRadii.size(); ++i) {
                     result.append(separator);
                     result.append(verticalRadii[i]);
                 }
             }
         }
     }
     result.append(')');
 
@@ skipping 59 matching lines @@
     visitor->trace(m_left);
     visitor->trace(m_topLeftRadius);
     visitor->trace(m_topRightRadius);
     visitor->trace(m_bottomRightRadius);
     visitor->trace(m_bottomLeftRadius);
     CSSValue::traceAfterDispatch(visitor);
 }
 
 } // namespace blink