First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/private_test.dart

Index: tests/compiler/dart2js/private_test.dart
diff --git a/tests/compiler/dart2js/private_test.dart b/tests/compiler/dart2js/private_test.dart
index c8918a70f04f470327b9d1370ed3b88fb605ca8c..e2507a25f37725283d233d918d047057654bd8a7 100644
--- a/tests/compiler/dart2js/private_test.dart
+++ b/tests/compiler/dart2js/private_test.dart
@@ -68,8 +68,9 @@ void analyze(String text, [expectedWarnings]) {
                   ''';
   Uri uri = Uri.parse('src:public');
   compiler.registerSource(uri, source);
-  compiler.runCompiler(uri);
-  compareWarningKinds(text, expectedWarnings, compiler.warnings);
+  compiler.runCompiler(uri).then((_) {
+    compareWarningKinds(text, expectedWarnings, compiler.warnings);
+  });
 }
 
 void main() {