First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/dead_code_test.dart

Index: tests/compiler/dart2js/dead_code_test.dart
diff --git a/tests/compiler/dart2js/dead_code_test.dart b/tests/compiler/dart2js/dead_code_test.dart
index 993d7e9505a471bdbaabe642020eb8c743426fde..4736a292e067392f5c716a167f09a50a3983bed2 100644
--- a/tests/compiler/dart2js/dead_code_test.dart
+++ b/tests/compiler/dart2js/dead_code_test.dart
@@ -16,6 +16,7 @@ foo(a) {
 ''';
 
 main() {
-  String generated = compileAll(TEST);
-  Expect.isFalse(generated.contains('return 42'), 'dead code not eliminated');
+  compileAll(TEST).then((generated) {
+    Expect.isFalse(generated.contains('return 42'), 'dead code not eliminated');
+  });
 }