Fix scanning of unterminated strings

pkg/front_end/testcases/regress/issue_29976.dart.direct.expect

Index: pkg/front_end/testcases/regress/issue_29976.dart.direct.expect
diff --git a/pkg/front_end/testcases/regress/issue_29976.dart.direct.expect b/pkg/front_end/testcases/regress/issue_29976.dart.direct.expect
new file mode 100644
index 0000000000000000000000000000000000000000..f2faee3c12a950cba7384ca72acb48954755167c
--- /dev/null
+++ b/pkg/front_end/testcases/regress/issue_29976.dart.direct.expect
@@ -0,0 +1,7 @@
+library;
+import self as self;
+
+static method main() → dynamic {
+  throw "pkg/front_end/testcases/regress/issue_29976.dart:10:1: Error: Expected a declaration, but got '\"'.\n\n^";

[ahe, 2017/08/01 14:19:57]

I don't think this is the expectation we really want. Should we delete this (and
other expectation files that throw a string) from this CL and mark the test as
failing?

[danrubel, 2017/08/01 21:23:19]

What do we expect in this situation?
Should we update this file to match what we expect?

+}
+