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

Source/core/css/CSSKeyframesRule.cpp

Index: Source/core/css/CSSKeyframesRule.cpp
diff --git a/Source/core/css/CSSKeyframesRule.cpp b/Source/core/css/CSSKeyframesRule.cpp
index 50d0ea5933d6f278f12a72bab8a4eec10e14cc57..8700d81922bafd2a0a6da16d6988c57f56c7fbfd 100644
--- a/Source/core/css/CSSKeyframesRule.cpp
+++ b/Source/core/css/CSSKeyframesRule.cpp
@@ -163,19 +163,19 @@ String CSSKeyframesRule::cssText() const
 {
     StringBuilder result;
     if (isVendorPrefixed())
-        result.append("@-webkit-keyframes ");
+        result.appendLiteral("@-webkit-keyframes ");
     else
-        result.append("@keyframes ");
+        result.appendLiteral("@keyframes ");
     result.append(name());
-    result.append(" { \n");
+    result.appendLiteral(" { \n");
 
     unsigned size = length();
     for (unsigned i = 0; i < size; ++i) {
-        result.append("  ");
+        result.appendLiteral("  ");
         result.append(m_keyframesRule->keyframes()[i]->cssText());
-        result.append("\n");
+        result.append('\n');
     }
-    result.append("}");
+    result.append('}');
     return result.toString();
 }