Add DartType.treatAsRaw to treat List<dynamic> as List in the backend.

tests/compiler/dart2js/type_representation_test.dart

Index: tests/compiler/dart2js/type_representation_test.dart
diff --git a/tests/compiler/dart2js/type_representation_test.dart b/tests/compiler/dart2js/type_representation_test.dart
index 5e6b7c5e2885ebd95e1c949c08a5d55b3214f2a3..e22297120c8e03d7e6b3e54afce52ef664cb77d7 100644
--- a/tests/compiler/dart2js/type_representation_test.dart
+++ b/tests/compiler/dart2js/type_representation_test.dart
@@ -94,7 +94,7 @@ void testTypeRepresentations() {
     // List
     expect('$List_rep', List_.rawType);
     // List<dynamic>
-    expect('[$List_rep, null]', instantiate(List_, [dynamic_]));
+    expect('$List_rep', instantiate(List_, [dynamic_]));
     // List<int>
     expect('[$List_rep, $int_rep]', instantiate(List_, [int_]));
     // List<Typedef>
@@ -102,11 +102,12 @@ void testTypeRepresentations() {
         instantiate(List_, [Typedef_]));
 
     // Map<K,V>
-    expect('[$Map_rep, $Map_K_rep, $Map_V_rep]', Map_.computeType(env.compiler));
+    expect('[$Map_rep, $Map_K_rep, $Map_V_rep]',
+           Map_.computeType(env.compiler));
     // Map
     expect('$Map_rep', Map_.rawType);
     // Map<dynamic,dynamic>
-    expect('[$Map_rep, null, null]', instantiate(Map_, [dynamic_, dynamic_]));
+    expect('$Map_rep', instantiate(Map_, [dynamic_, dynamic_]));
     // Map<int,String>
     expect('[$Map_rep, $int_rep, $String_rep]',
         instantiate(Map_, [int_, String_]));