Use precompiled dependencies in pub.

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

Index: sdk/lib/_internal/pub/lib/src/barback/transformer_cache.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/transformer_cache.dart b/sdk/lib/_internal/pub/lib/src/barback/transformer_cache.dart
index d51e901bc36acd9e3bc4c79537a5d0b4424906c0..5433ce159335954619e8fa6c2588190112a69b42 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/transformer_cache.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/transformer_cache.dart
@@ -10,9 +10,7 @@ import '../io.dart';
 import '../log.dart' as log;
 import '../package_graph.dart';
 import '../sdk.dart' as sdk;
-import '../source/cached.dart';
 import '../utils.dart';
-import 'asset_environment.dart';
 import 'transformer_id.dart';
 
 /// A cache for managing a snapshot of the first "stage" of transformers to
@@ -51,7 +49,7 @@ class TransformerCache {
   /// This may modify the cache.
   TransformerCache.load(PackageGraph graph)
       : _graph = graph,
-        _dir = p.join(graph.entrypoint.root.dir, ".pub/transformers") {
+        _dir = graph.entrypoint.root.path(".pub/transformers") {
     _oldTransformers = _parseManifest();
   }