Update handling of multiline strings to specification.

tests/language/multiline_newline_crlf.dart

Index: tests/language/multiline_newline_crlf.dart
diff --git a/tests/language/multiline_newline_crlf.dart b/tests/language/multiline_newline_crlf.dart
index 64cd255a70d0630031e5b78eb8c0969dff4204c6..c8b78ded6c512e638a48856ca14f552979e34efb 100644
--- a/tests/language/multiline_newline_crlf.dart
+++ b/tests/language/multiline_newline_crlf.dart
@@ -13,3 +13,13 @@ var nonConstantMultilineString = """
 a
 b
 """;
+
+const constantRawMultilineString = r"""
+\a
+\b
+""";
+
+var nonConstantRawMultilineString = r"""
+\a
+\b
+""";