Improve parallelism when loading transformer plugins.

sdk/lib/_internal/pub/lib/src/package_graph.dart

Index: sdk/lib/_internal/pub/lib/src/package_graph.dart
diff --git a/sdk/lib/_internal/pub/lib/src/package_graph.dart b/sdk/lib/_internal/pub/lib/src/package_graph.dart
index 47e1349bfec2cd9679e2844ca483dc6b08e7a18f..14913787b95be9a5c9a70ad98a672c5762a03332 100644
--- a/sdk/lib/_internal/pub/lib/src/package_graph.dart
+++ b/sdk/lib/_internal/pub/lib/src/package_graph.dart
@@ -25,22 +25,4 @@ class PackageGraph {
   final Map<String, Package> packages;
 
   PackageGraph(this.entrypoint, this.lockFile, this.packages);
-
-  /// Returns the set of transitive dependencies of the package named
-  /// [packageName].
-  Set<Package> transitiveDependencies(String packageName) {
-    var seen = new Set<Package>();
-    traverse(Package package) {
-      if (seen.contains(package)) return;
-      seen.add(package);
-      for (var dep in package.dependencies) {
-        traverse(packages[dep.name]);
-      }
-    }
-
-    var package = packages[packageName];
-    traverse(package);
-    seen.remove(package);
-    return seen;
-  }
 }