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

third_party/WebKit/Source/modules/accessibility/AXObject.cpp

 /*
  * Copyright (C) 2008, 2009, 2011 Apple Inc. 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.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 847 matching lines @@
 
     for (const auto& element : elements) {
         AXObject* axElement = axObjectCache().getOrCreate(element);
         if (axElement) {
             foundValidElement = true;
 
             String result = recursiveTextAlternative(*axElement, inAriaLabelledbyTraversal, visited);
             localRelatedObjects.append(new NameSourceRelatedObject(axElement, result));
             if (!result.isEmpty()) {
                 if (!accumulatedText.isEmpty())
-                    accumulatedText.append(" ");
+                    accumulatedText.append(' ');
                 accumulatedText.append(result);
             }
         }
     }
     if (!foundValidElement)
         return String();
     if (relatedObjects)
         *relatedObjects = localRelatedObjects;
     return accumulatedText.toString();
 }
@@ skipping 869 matching lines @@
 
 DEFINE_TRACE(AXObject)
 {
     visitor->trace(m_children);
     visitor->trace(m_parent);
     visitor->trace(m_cachedLiveRegionRoot);
     visitor->trace(m_axObjectCache);
 }
 
 } // namespace blink