Introduce DartType.unaliased to avoid use of Resolution in the backend.

pkg/compiler/lib/src/deferred_load.dart

Index: pkg/compiler/lib/src/deferred_load.dart
diff --git a/pkg/compiler/lib/src/deferred_load.dart b/pkg/compiler/lib/src/deferred_load.dart
index d0f312032be85144ac8ab5af99f8bc0ebba8ec60..759252748d2b835efca8a699f43d17e410485e8e 100644
--- a/pkg/compiler/lib/src/deferred_load.dart
+++ b/pkg/compiler/lib/src/deferred_load.dart
@@ -6,8 +6,6 @@ library deferred_load;
 
 import 'common/backend_api.dart' show
     Backend;
-import 'common/resolution.dart' show
-    Resolution;
 import 'common/tasks.dart' show
     CompilerTask;
 import 'compiler.dart' show
@@ -285,7 +283,7 @@ class DeferredLoadTask extends CompilerTask {
         collectTypeDependencies(type.returnType);
       } else if (type is TypedefType) {
         elements.add(type.element);
-        collectTypeDependencies(type.unalias(compiler.resolution));
+        collectTypeDependencies(type.unaliased);
       } else if (type is InterfaceType) {
         elements.add(type.element);
       }