Use precompiled dependencies in pub.

sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart

Index: sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart b/sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart
index 3b156de5fccd80ab632e8773fbb69809541d5dd1..89a3761383c67e43bf88b840c776d3ce3bbfc8e5 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart
@@ -28,8 +28,7 @@ import 'transformers_needed_by_transformers.dart';
 Future loadAllTransformers(AssetEnvironment environment,
     BarbackServer transformerServer) async {
   var transformersNeededByTransformers =
-      computeTransformersNeededByTransformers(environment.graph,
-          packages: environment.packages);
+      computeTransformersNeededByTransformers(environment.graph);
 
   var buffer = new StringBuffer();
   buffer.writeln("Transformer dependencies:");
@@ -44,15 +43,14 @@ Future loadAllTransformers(AssetEnvironment environment,
 
   var stagedTransformers = _stageTransformers(transformersNeededByTransformers);
 
-  var packagesThatUseTransformers =
-      _packagesThatUseTransformers(environment.graph);
+  var packagesThatUseTransformers = _packagesThatUseTransformers(environment);
 
   var loader = new TransformerLoader(environment, transformerServer);
 
   // Add a rewrite transformer for each package, so that we can resolve
   // "package:" imports while loading transformers.
   var rewrite = new RewriteImportTransformer();
-  for (var package in environment.packages) {
+  for (var package in environment.graph.packages.keys) {
     environment.barback.updateTransformers(package, [[rewrite]]);
   }
   environment.barback.updateTransformers(r'$pub', [[rewrite]]);
@@ -145,9 +143,9 @@ List<Set<TransformerId>> _stageTransformers(
 /// Returns a map from transformer ids to all packages in [graph] that use each
 /// transformer.
 Map<TransformerId, Set<String>> _packagesThatUseTransformers(
-    PackageGraph graph) {
+    AssetEnvironment environment) {
   var results = {};
-  for (var package in graph.packages.values) {
+  for (var package in environment.graph.packages.values) {
     for (var phase in package.pubspec.transformers) {
       for (var config in phase) {
         results.putIfAbsent(config.id, () => new Set()).add(package.name);