Invoke dart2js lazily when using pub serve.

sdk/lib/_internal/pub/test/transformer/dart2js/does_not_compile_until_its_output_is_requested_test.dart

Index: sdk/lib/_internal/pub/test/transformer/dart2js/does_not_compile_until_its_output_is_requested_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/dart2js/compiles_generated_dart_file_test.dart b/sdk/lib/_internal/pub/test/transformer/dart2js/does_not_compile_until_its_output_is_requested_test.dart
similarity index 52%
copy from sdk/lib/_internal/pub/test/transformer/dart2js/compiles_generated_dart_file_test.dart
copy to sdk/lib/_internal/pub/test/transformer/dart2js/does_not_compile_until_its_output_is_requested_test.dart
index 9d73a053644c600031475df18b295104b76925ad..e71c925b9ea1c7cf6004166499bed85bb9bd4cc1 100644
--- a/sdk/lib/_internal/pub/test/transformer/dart2js/compiles_generated_dart_file_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/dart2js/does_not_compile_until_its_output_is_requested_test.dart
@@ -1,4 +1,4 @@
-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.file
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS d.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.
 
@@ -12,28 +12,27 @@ import '../../serve/utils.dart';
 
 main() {
   initConfig();
-  integration("compiles a generated Dart file to JS", () {
+  integration("does not compile until its output is requested", () {
     d.dir(appPath, [
       d.pubspec({
         "name": "myapp",
         "version": "0.0.1",
-        "transformers": ["myapp/transformer"]
       }),
-      d.dir("lib", [
-        d.file("transformer.dart", dartTransformer("munge"))
-      ]),
       d.dir("web", [
-        d.file("main.dart", """
-const TOKEN = "before";
-void main() => print(TOKEN);
-""")
+        d.file("syntax-error.dart", "syntax error")
       ])
     ]).create();
 
     createLockFile('myapp', pkg: ['barback']);
 
-    pubServe();
-    requestShouldSucceed("main.dart.js", contains("(before, munge)"));
+    var server = pubServe();
+    expect(server.nextLine(),
+        completion(equals("Build completed successfully")));

[Bob Nystrom, 2014/02/11 19:08:47]

This highlights an interesting corner of the user experience. We may want to
change the wording of this message now since the user could infer it to mean
none of their assets have errors, which isn't the case.

Maybe it should be "Build finished" or something?

+
+    // Once we request the output, it should start compiling and fail.
+    requestShould404("syntax-error.dart.js");
+    expect(server.nextLine(),
+        completion(equals("Build completed with 1 errors.")));
     endPubServe();
   });
 }