First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/no_duplicate_stub_test.dart

Index: tests/compiler/dart2js/no_duplicate_stub_test.dart
diff --git a/tests/compiler/dart2js/no_duplicate_stub_test.dart b/tests/compiler/dart2js/no_duplicate_stub_test.dart
index 3213529a77f9861e68b7af1dc8656ded6b4498f2..4f7d0b6dd85dce3cc0af6fed368842a85da19402 100644
--- a/tests/compiler/dart2js/no_duplicate_stub_test.dart
+++ b/tests/compiler/dart2js/no_duplicate_stub_test.dart
@@ -28,8 +28,9 @@ baz(a) {
 """;
 
 main() {
-  String generated = compileAll(TEST);
-  RegExp regexp = new RegExp('foo\\\$1\\\$a: function');
-  Iterator<Match> matches = regexp.allMatches(generated).iterator;
-  checkNumberOfMatches(matches, 1);
+  compileAll(TEST).then((generated) {
+    RegExp regexp = new RegExp('foo\\\$1\\\$a: function');
+    Iterator<Match> matches = regexp.allMatches(generated).iterator;
+    checkNumberOfMatches(matches, 1);
+  });
 }