Migrate test block 8 to Dart 2.0.

tests/corelib_2/format_exception_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library format_exception_test;
 
 import "package:expect/expect.dart";
 
 test(exn, message, source, offset, toString) {
   Expect.equals(message, exn.message);
@@ skipping 65 matching lines @@
   var half = longline.length ~/ 2;
   e = new FormatException("message", longsource, line10 + half);
   test(
       e,
       "message",
       longsource,
       line10 + half,
       "FormatException: message (at line 10, character ${half + 1})\n"
       "...${longline.substring(half - 36, half + 36)}...\n"
       "${' ' * 39}^\n");
+
+  var sourceNL = "\nsource with leading NL";
+  e = new FormatException("message", sourceNL, 2);
+  test(
+      e,
+      "message",
+      sourceNL,
+      2,
+      "FormatException: message (at line 2, character 2)\n"
+      "source with leading NL\n"
+      " ^\n");
+
+  var sourceNL2 = "\n\nsource with leading NL";
+  e = new FormatException("message", sourceNL2, 2);
+  test(
+      e,
+      "message",
+      sourceNL2,
+      2,
+      "FormatException: message (at line 3, character 1)\n"
+      "source with leading NL\n"
+      "^\n");
 }