Don't try to load unnecessary transformers when precompiling executables.

sdk/lib/_internal/pub_generated/test/snapshot/doesnt_load_irrelevant_transformers_test.dart

Index: sdk/lib/_internal/pub_generated/test/snapshot/doesnt_load_irrelevant_transformers_test.dart
diff --git a/sdk/lib/_internal/pub_generated/test/snapshot/snapshots_transformed_code_test.dart b/sdk/lib/_internal/pub_generated/test/snapshot/doesnt_load_irrelevant_transformers_test.dart
similarity index 52%
copy from sdk/lib/_internal/pub_generated/test/snapshot/snapshots_transformed_code_test.dart
copy to sdk/lib/_internal/pub_generated/test/snapshot/doesnt_load_irrelevant_transformers_test.dart
index 681d1025787095497fd85981672c6acd872a735d..319882bc885e26ce362c47c6bf726fdfb67191d5 100644
--- a/sdk/lib/_internal/pub_generated/test/snapshot/snapshots_transformed_code_test.dart
+++ b/sdk/lib/_internal/pub_generated/test/snapshot/doesnt_load_irrelevant_transformers_test.dart
@@ -3,45 +3,37 @@ import 'package:path/path.dart' as p;
 import 'package:scheduled_test/scheduled_test.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
-const REPLACE_TRANSFORMER = """
+const BROKEN_TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
-class ReplaceTransformer extends Transformer {
-  ReplaceTransformer.asPlugin();
+class BrokenTransformer extends Transformer {
+  BrokenTransformer.asPlugin();
 
-  String get allowedExtensions => '.dart';
-
-  Future apply(Transform transform) {
-    return transform.primaryInput.readAsString().then((contents) {
-      transform.addOutput(new Asset.fromString(transform.primaryInput.id,
-          contents.replaceAll("REPLACE ME", "hello!")));
-    });
-  }
-}
+  // This file intentionally has a syntax error so that any attempt to load it
+  // will crash.
 """;
 main() {
   initConfig();
   integration("snapshots the transformed version of an executable", () {
     servePackages((builder) {
       builder.serveRepoPackage('barback');
-      builder.serve("foo", "1.2.3", deps: {
-        "barback": "any"
-      }, pubspec: {
-        'transformers': ['foo']
-      },
+      builder.serve(
+          "foo",
+          "1.2.3",
           contents: [
-              d.dir("lib", [d.file("foo.dart", REPLACE_TRANSFORMER)]),
-              d.dir("bin", [d.file("hello.dart", """
-final message = 'REPLACE ME';
-
-void main() => print(message);
-""")])]);
+              d.dir("bin", [d.file("hello.dart", "void main() => print('hello!');")])]);
     });
-    d.appDir({
-      "foo": "1.2.3"
-    }).create();
+    d.dir(appPath, [d.pubspec({
+        "name": "myapp",
+        "dependencies": {
+          "foo": "1.2.3",
+          "barback": "any"
+        },
+        "transformers": ["myapp"]
+      }),
+          d.dir("lib", [d.file("transformer.dart", BROKEN_TRANSFORMER)])]).create();
     pubGet(output: contains("Precompiled foo:hello."));
     d.dir(
         p.join(appPath, '.pub', 'bin'),