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

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

Index: sdk/lib/_internal/pub/lib/src/global_packages.dart
diff --git a/sdk/lib/_internal/pub/lib/src/global_packages.dart b/sdk/lib/_internal/pub/lib/src/global_packages.dart
index ed70d5b17fe5b39d49ee97673d6c837b297fd6b3..479a486c528d9081d52ce22d4f0b9a6d8e1553fa 100644
--- a/sdk/lib/_internal/pub/lib/src/global_packages.dart
+++ b/sdk/lib/_internal/pub/lib/src/global_packages.dart
@@ -197,8 +197,11 @@ class GlobalPackages {
       var binDir = p.join(_directory, package, 'bin');
       cleanDir(binDir);
 
-      var environment = await AssetEnvironment.create(entrypoint,
-          BarbackMode.RELEASE, useDart2JS: false);
+      var graph = await entrypoint.loadPackageGraph();
+      var environment = await AssetEnvironment.create(
+          entrypoint, BarbackMode.RELEASE,
+          entrypoints: graph.packages[package].executableIds,
+          useDart2JS: false);
       environment.barback.errors.listen((error) {
         log.error(log.red("Build error:\n$error"));
       });