Don't load transformers that aren't going to be used for an executable.

sdk/lib/_internal/pub_generated/test/dependency_computer/utils.dart

Index: sdk/lib/_internal/pub_generated/test/dependency_computer/utils.dart
diff --git a/sdk/lib/_internal/pub_generated/test/transformers_needed_by_transformers/utils.dart b/sdk/lib/_internal/pub_generated/test/dependency_computer/utils.dart
similarity index 76%
rename from sdk/lib/_internal/pub_generated/test/transformers_needed_by_transformers/utils.dart
rename to sdk/lib/_internal/pub_generated/test/dependency_computer/utils.dart
index 53829617e7614005673ad7176f8e718297da3f98..ee048b1ed83dabb7145feb6595786306dd517737 100644
--- a/sdk/lib/_internal/pub_generated/test/transformers_needed_by_transformers/utils.dart
+++ b/sdk/lib/_internal/pub_generated/test/dependency_computer/utils.dart
@@ -1,8 +1,9 @@
 library pub_tests;
+import 'package:barback/barback.dart';
 import 'package:path/path.dart' as p;
 import 'package:scheduled_test/scheduled_test.dart';
 import '../../lib/src/barback/cycle_exception.dart';
-import '../../lib/src/barback/transformers_needed_by_transformers.dart';
+import '../../lib/src/barback/dependency_computer.dart';
 import '../../lib/src/entrypoint.dart';
 import '../../lib/src/io.dart';
 import '../../lib/src/package.dart';
@@ -14,8 +15,9 @@ import '../test_pub.dart';
 void expectDependencies(Map<String, Iterable<String>> expected) {
   expected = mapMap(expected, value: (_, ids) => ids.toSet());
   schedule(() {
+    var computer = new DependencyComputer(_loadPackageGraph());
     var result = mapMap(
-        computeTransformersNeededByTransformers(_loadPackageGraph()),
+        computer.transformersNeededByTransformers(),
         key: (id, _) => id.toString(),
         value: (_, ids) => ids.map((id) => id.toString()).toSet());
     expect(result, equals(expected));
@@ -23,9 +25,10 @@ void expectDependencies(Map<String, Iterable<String>> expected) {
 }
 void expectException(matcher) {
   schedule(() {
-    expect(
-        () => computeTransformersNeededByTransformers(_loadPackageGraph()),
-        throwsA(matcher));
+    expect(() {
+      var computer = new DependencyComputer(_loadPackageGraph());
+      computer.transformersNeededByTransformers();
+    }, throwsA(matcher));
   }, "expect an exception: $matcher");
 }
 void expectCycleException(Iterable<String> steps) {
@@ -35,6 +38,15 @@ void expectCycleException(Iterable<String> steps) {
     return true;
   }, "cycle exception:\n${steps.map((step) => "  $step").join("\n")}"));
 }
+void expectLibraryDependencies(String id, Iterable<String> expected) {
+  expected = expected.toSet();
+  schedule(() {
+    var computer = new DependencyComputer(_loadPackageGraph());
+    var result = computer.transformersNeededByLibrary(
+        new AssetId.parse(id)).map((id) => id.toString()).toSet();
+    expect(result, equals(expected));
+  }, "expect dependencies to match $expected");
+}
 PackageGraph _loadPackageGraph() {
   var packages = {};
   var systemCache = new SystemCache(p.join(sandboxDir, cachePath));