Handle multiline interpolated strings in line-based scanner.

dart/tests/try/paste_content_rewriting_test.dart

Index: dart/tests/try/paste_content_rewriting_test.dart
diff --git a/dart/tests/try/paste_content_rewriting_test.dart b/dart/tests/try/paste_content_rewriting_test.dart
index 6583c75f06720c4db5aebce3553b7eec63dab6a8..1c7b2b2dfc0e1e3b340f07109c7068530c3b75e8 100644
--- a/dart/tests/try/paste_content_rewriting_test.dart
+++ b/dart/tests/try/paste_content_rewriting_test.dart
@@ -31,6 +31,15 @@ const Map<String, String> tests = const <String, String> {
   'r"""\n\n\'"""': 'r"""\n\n\'"""',
   '"': '<DIAGNOSTIC>"</DIAGNOSTIC>',
   '/**\n*/': '/**\n*/',
+
+  // The following case tests that single line strings can span multiple lines
+  // via ${}. The string is constructed so that it is possible to tell if the
+  // line-bases scanner (incorrectly) reverses the order of the string quotes
+  // in its state string. The example string is a complicated way of writing:
+  // '[[{{}: {}}]]'. See also
+  // tests/language/string_interpolation_newline_test.dart.
+  '"\${ [ "\${ [ \'\${ { \'\${\n{\n} }\' : {\n} } }\' ] }" ] }"':
+  '"\${ [ "\${ [ \'\${ { \'\${\n{\n} }\' : {\n} } }\' ] }" ] }"',
 };
 
 List<Node> queryDiagnosticNodes() {