Fixing string compile-time constant evaluation

frog/utils.dart

Index: frog/utils.dart
diff --git a/frog/utils.dart b/frog/utils.dart
index 657349a6cf0c7d20ca3ed3c89286791ad5b32128..d9853f8f151b6ed85dd7f3cd6dc12df6a12f89bd 100644
--- a/frog/utils.dart
+++ b/frog/utils.dart
@@ -70,6 +70,15 @@ bool isRawMultilineString(String text) {
   return text.startsWith('@"""') || text.startsWith("@'''");
 }
 
+/**
+ * Convert a single-quote string to be a double-quote string by replacing " with
+ * \" and \' with '.
+ */
+String toDoubleQuote(String s) {
+  return s.replaceAll('"', '\\"').replaceAll("\\'", "'");
+}
+
+
 // TODO(jmesserly): it'd be nice to deal with this in the tokenizer, rather than
 // taking another pass over the string.
 String parseStringLiteral(String lit) {