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

Source/core/rendering/RenderText.cpp

Index: Source/core/rendering/RenderText.cpp
diff --git a/Source/core/rendering/RenderText.cpp b/Source/core/rendering/RenderText.cpp
index 94a7453fd651e68d124486d338d3af51913f0c68..64273e8b1c48066882c0d0a8d8ba42b658de039f 100644
--- a/Source/core/rendering/RenderText.cpp
+++ b/Source/core/rendering/RenderText.cpp
@@ -318,7 +318,7 @@ String RenderText::plainText() const
         String text = m_text.substring(textBox->start(), textBox->len()).simplifyWhiteSpace(WTF::DoNotStripWhiteSpace);
         plainTextBuilder.append(text);
         if (textBox->nextTextBox() && textBox->nextTextBox()->start() > textBox->end() && text.length() && !text.right(1).containsOnlyWhitespace())
-            plainTextBuilder.append(" ");
+            plainTextBuilder.append(' ');
     }
     return plainTextBuilder.toString();
 }