Support declaring and lazy transformers in pub.

sdk/lib/_internal/pub/test/serve/supports_user_defined_lazy_transformers_test.dart

Index: sdk/lib/_internal/pub/test/serve/supports_user_defined_lazy_transformers_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/can_use_consume_primary_test.dart b/sdk/lib/_internal/pub/test/serve/supports_user_defined_lazy_transformers_test.dart
similarity index 57%
copy from sdk/lib/_internal/pub/test/transformer/can_use_consume_primary_test.dart
copy to sdk/lib/_internal/pub/test/serve/supports_user_defined_lazy_transformers_test.dart
index 9b41b2bbc5905412e31e2c3d02224973d5b1ff64..fd88315bda6f89e7040bed937432f84bfa8565db 100644
--- a/sdk/lib/_internal/pub/test/transformer/can_use_consume_primary_test.dart
+++ b/sdk/lib/_internal/pub/test/serve/supports_user_defined_lazy_transformers_test.dart
@@ -6,32 +6,36 @@ library pub_tests;
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
-import '../serve/utils.dart';
+import 'utils.dart';
 
 const TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
-class RewriteTransformer extends Transformer {
-  RewriteTransformer.asPlugin();
+class LazyRewriteTransformer extends Transformer implements LazyTransformer {
+  LazyRewriteTransformer.asPlugin();
 
   String get allowedExtensions => '.txt';
 
   Future apply(Transform transform) {
-    transform.consumePrimary();
+    transform.logger.info('Rewriting \${transform.primaryInput.id}.');
     return transform.primaryInput.readAsString().then((contents) {
       var id = transform.primaryInput.id.changeExtension(".out");
-      var asset = new Asset.fromString(id, "\$contents.out");
-      transform.addOutput(asset);
+      transform.addOutput(new Asset.fromString(id, "\$contents.out"));
     });
   }
+
+  Future declareOutputs(DeclaringTransform transform) {
+    transform.declareOutput(transform.primaryId.changeExtension(".out"));
+    return new Future.value();
+  }
 }
 """;
 
 main() {
   initConfig();
-  integration("a transform can use consumePrimary", () {
+  integration("supports a user-defined lazy transformer", () {
     d.dir(appPath, [
       d.pubspec({
         "name": "myapp",
@@ -47,9 +51,14 @@ main() {
 
     createLockFile('myapp', pkg: ['barback']);
 
-    pubServe();
+    var server = pubServe();
+    // The build should complete without the transformer logging anything.
+    server.stdout.expect('Build completed successfully');
+
     requestShouldSucceed("foo.out", "foo.out");
-    requestShould404("foo.txt");
+    server.stdout.expect(emitsLines(
+        '[Info from LazyRewrite]:\n'
+        'Rewriting myapp|web/foo.txt.'));
     endPubServe();
   });
 }