Use precompiled dependencies in pub.

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

Index: sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart b/sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart
index 36ec86594aac6f6093217fd7971613e8156d15dd..72f22928d982d139d91170cc24212b27280ed607 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart
@@ -21,10 +21,9 @@ class PubPackageProvider implements PackageProvider {
   final PackageGraph _graph;
   final List<String> packages;
 
-  PubPackageProvider(PackageGraph graph, [Iterable<String> packages])
+  PubPackageProvider(PackageGraph graph)
       : _graph = graph,
-        packages = [r"$pub", r"$sdk"]
-            ..addAll(packages == null ? graph.packages.keys : packages);
+        packages = [r"$pub", r"$sdk"]..addAll(graph.packages.keys);
 
   Future<Asset> getAsset(AssetId id) {
     // "$pub" is a psuedo-package that allows pub's transformer-loading
@@ -67,7 +66,7 @@ class PubPackageProvider implements PackageProvider {
     }
 
     var nativePath = path.fromUri(id.path);
-    var file = path.join(_graph.packages[id.package].dir, nativePath);
+    var file = _graph.packages[id.package].path(nativePath);
     return new Future.value(new Asset.fromPath(id, file));
   }
 }