Use StringBuilder::appendLiteral() / StringBuilder::append(char) when possible

Source/platform/animation/TimingFunction.cpp

Index: Source/platform/animation/TimingFunction.cpp
diff --git a/Source/platform/animation/TimingFunction.cpp b/Source/platform/animation/TimingFunction.cpp
index 69f427f21aa018e5e777d1a3dd7054e788da712c..e0ebc48f0a33ca9c15a23afe908cc11911194ec2 100644
--- a/Source/platform/animation/TimingFunction.cpp
+++ b/Source/platform/animation/TimingFunction.cpp
@@ -125,15 +125,15 @@ String StepsTimingFunction::toString() const
         builder.append("steps(" + String::numberToStringECMAScript(this->numberOfSteps()) + ", ");
 
         if (this->stepAtPosition() == StepsTimingFunction::StepAtStart)
-            builder.append("start");
+            builder.appendLiteral("start");
         else if (this->stepAtPosition() == StepsTimingFunction::StepAtMiddle)
-            builder.append("middle");
+            builder.appendLiteral("middle");
         else if (this->stepAtPosition() == StepsTimingFunction::StepAtEnd)
-            builder.append("end");
+            builder.appendLiteral("end");
         else
             ASSERT_NOT_REACHED();
 
-        builder.append(")");
+        builder.append(')');
         break;
     default:
         ASSERT_NOT_REACHED();