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

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/css/CSSGridAutoRepeatValue.h"
 
 #include "wtf/text/StringBuilder.h"
 
 namespace blink {
 
 String CSSGridAutoRepeatValue::customCSSText() const
 {
     StringBuilder result;
     result.append("repeat(");
     result.append(getValueName(autoRepeatID()));
     result.append(", ");
     result.append(CSSValueList::customCSSText());
-    result.append(")");
+    result.append(')');
     return result.toString();
 }
 
 } // namespace blink