Support all Transform methods on ForeignTransform.

sdk/lib/_internal/pub/test/transformer/can_use_read_input_as_string_test.dart

Index: sdk/lib/_internal/pub/test/transformer/can_use_read_input_as_string_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/prints_a_transform_interface_error_test.dart b/sdk/lib/_internal/pub/test/transformer/can_use_read_input_as_string_test.dart
similarity index 64%
copy from sdk/lib/_internal/pub/test/transformer/prints_a_transform_interface_error_test.dart
copy to sdk/lib/_internal/pub/test/transformer/can_use_read_input_as_string_test.dart
index d84ff22f1f91532bd9c0f35483897c67a3a2d502..0084d5c8105331a836391d2652ce764ef03551f3 100644
--- a/sdk/lib/_internal/pub/test/transformer/prints_a_transform_interface_error_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/can_use_read_input_as_string_test.dart
@@ -8,9 +8,7 @@ import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import '../serve/utils.dart';
 
-import 'package:scheduled_test/scheduled_test.dart';
-
-final transformer = """
+const TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
@@ -19,19 +17,27 @@ class RewriteTransformer extends Transformer {
   RewriteTransformer.asPlugin();
 
   String get allowedExtensions => '.txt';
+
+  Future apply(Transform transform) {
+    return transform.readInputAsString(transform.primaryInput.id)
+        .then((contents) {
+      var id = transform.primaryInput.id.changeExtension(".out");
+      transform.addOutput(new Asset.fromString(id, "\$contents.out"));
+    });
+  }
 }
 """;
 
 main() {
   initConfig();
-  integration("prints a transform interface error", () {
+  integration("a transform can use readInputAsString", () {
     d.dir(appPath, [
       d.pubspec({
         "name": "myapp",
         "transformers": ["myapp/src/transformer"]
       }),
       d.dir("lib", [d.dir("src", [
-        d.file("transformer.dart", transformer)
+        d.file("transformer.dart", TRANSFORMER)
       ])]),
       d.dir("web", [
         d.file("foo.txt", "foo")
@@ -40,11 +46,8 @@ main() {
 
     createLockFile('myapp', pkg: ['barback']);
 
-    var server = startPubServe();
-    expect(server.nextErrLine(), completion(equals('Build error:')));
-    expect(server.nextErrLine(), completion(equals("Transform Rewrite on "
-        "myapp|web/foo.txt threw error: Class 'RewriteTransformer' has no "
-        "instance method 'apply'.")));
+    startPubServe();
+    requestShouldSucceed("foo.out", "foo.out");
     endPubServe();
   });
 }