Add support for source maps in deferred libraries.

tests/compiler/dart2js/source_map_deferred_validator_test_lib.dart

Index: tests/compiler/dart2js/source_map_deferred_validator_test_lib.dart
diff --git a/tests/try/poi/data/interesting.dart b/tests/compiler/dart2js/source_map_deferred_validator_test_lib.dart
similarity index 71%
copy from tests/try/poi/data/interesting.dart
copy to tests/compiler/dart2js/source_map_deferred_validator_test_lib.dart
index 9f39d9d5d2eab4e0d7e6ad9be4a4c3c835fa7aa2..9ce7323f96c13b5ae2fdfd775fe26c56e291e7ad 100644
--- a/tests/try/poi/data/interesting.dart
+++ b/tests/compiler/dart2js/source_map_deferred_validator_test_lib.dart
@@ -2,13 +2,10 @@
 // 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 interesting;
-
-class Foo {
-  fisk() {
-  }
-  hest() {
+class HelloClass {
+  void printHello() {
+    () {
+      print('Hello World!');
+    }();
   }
 }
-
-main() {}