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

third_party/WebKit/Source/platform/text/DateTimeFormatTest.cpp

Index: third_party/WebKit/Source/platform/text/DateTimeFormatTest.cpp
diff --git a/third_party/WebKit/Source/platform/text/DateTimeFormatTest.cpp b/third_party/WebKit/Source/platform/text/DateTimeFormatTest.cpp
index cacbd786fbf8abc5ce39f6ece3dc95c07eedee08..53729df97d2e7b3975ea2c40080d225d379b88bd 100644
--- a/third_party/WebKit/Source/platform/text/DateTimeFormatTest.cpp
+++ b/third_party/WebKit/Source/platform/text/DateTimeFormatTest.cpp
@@ -147,10 +147,10 @@ public:
             builder.append("Tokens(");
             for (unsigned index = 0; index < m_tokens.size(); ++index) {
                 if (index)
-                    builder.append(",");
+                    builder.append(',');
                 builder.append(m_tokens[index].toString());
             }
-            builder.append(")");
+            builder.append(')');
             return builder.toString();
         }