Implement string interpolation up to SSA.

dart/frog/leg/tools/mini_parser.dart

Index: dart/frog/leg/tools/mini_parser.dart
diff --git a/dart/frog/leg/tools/mini_parser.dart b/dart/frog/leg/tools/mini_parser.dart
index 14ae9584ae2d55da791d99a7074b94d1712de794..2cfe260841cb5ac09cfa2b07108ed0f1d317d5d0 100644
--- a/dart/frog/leg/tools/mini_parser.dart
+++ b/dart/frog/leg/tools/mini_parser.dart
@@ -105,7 +105,12 @@ Token scan(MySourceFile source) {
     var message = ex.message;
     if (message is !String) message = "unexpected character";
     Token fakeToken = new Token($QUESTION, scanner.charOffset);
-    new MyListener(source).error(message, fakeToken);
+    try {
+      new MyListener(source).error(message, fakeToken);
+    } catch (ParserError ex) {
+      // TODO(ahe): Clean this up, don't throw exceptions.
+      print(ex);
+    }
     throw;
   }
 }