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

pkg/compiler/lib/src/js_emitter/native_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/native_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/native_emitter.dart b/pkg/compiler/lib/src/js_emitter/native_emitter.dart
index df8778df24427efc1b36ab67e4bc5e4a9ab2d5ef..d78ac6d1d7d0cae8889863f683ba4a5ef091adc7 100644
--- a/pkg/compiler/lib/src/js_emitter/native_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/native_emitter.dart
@@ -268,7 +268,7 @@ class NativeEmitter {
       // parameter that was not provided for this stub.
       for (jsAst.Parameter stubParameter in stubParameters) {
         if (stubParameter.name == name) {
-          DartType type = parameter.type.unalias(compiler.resolution);
+          DartType type = parameter.type.unaliased;
           if (type is FunctionType) {
             // The parameter type is a function type either directly or through
             // typedef(s).