Perform MixinFullResolution only for source libraries.

pkg/kernel/lib/target/vm.dart

Index: pkg/kernel/lib/target/vm.dart
diff --git a/pkg/kernel/lib/target/vm.dart b/pkg/kernel/lib/target/vm.dart
index 7959de5ccc933397e8dd79c2e5b5f123d44efc41..e8c7df1d5f7613e862dd20aa24a9d7c43b302f9f 100644
--- a/pkg/kernel/lib/target/vm.dart
+++ b/pkg/kernel/lib/target/vm.dart
@@ -57,7 +57,8 @@ class VmTarget extends Target {
   ClassHierarchy _hierarchy;
 
   void performModularTransformations(Program program) {
-    var mixins = new mix.MixinFullResolution(this)..transform(program);
+    var mixins = new mix.MixinFullResolution(this)
+      ..transform(program.libraries);
 
     _hierarchy = mixins.hierarchy;
   }