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

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

Index: sdk/lib/_internal/pub/lib/src/entrypoint.dart
diff --git a/sdk/lib/_internal/pub/lib/src/entrypoint.dart b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
index 5f3f7d1a6c43466f5e5ae718142513555a11b4c1..44f66066cd93e64e377d8a10465e944745f2761d 100644
--- a/sdk/lib/_internal/pub/lib/src/entrypoint.dart
+++ b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
@@ -265,8 +265,10 @@ class Entrypoint {
       var packagesToLoad =
           unionAll(executables.keys.map(graph.transitiveDependencies))
           .map((package) => package.name).toSet();
+      var executableIds = unionAll(executables.values.map((ids) => ids.toSet()));

[Bob Nystrom, 2014/09/24 23:42:47]

Long line.

[nweiz, 2014/09/25 00:13:15]

Done.

       var environment = await AssetEnvironment.create(this, BarbackMode.RELEASE,
           packages: packagesToLoad,
+          entrypoints: executableIds,
           useDart2JS: false);
       environment.barback.errors.listen((error) {
         log.error(log.red("Build error:\n$error"));