Fix --host-checked mode and add proper canBePrimitive method to HBoundedType.

sdk/lib/_internal/compiler/implementation/types/type_mask.dart

Index: sdk/lib/_internal/compiler/implementation/types/type_mask.dart
diff --git a/sdk/lib/_internal/compiler/implementation/types/type_mask.dart b/sdk/lib/_internal/compiler/implementation/types/type_mask.dart
index ffc8d906782f1c2024aa7d9c95ff85eb20d83048..828be8744b9c563b9ce50f852df71818b493a84e 100644
--- a/sdk/lib/_internal/compiler/implementation/types/type_mask.dart
+++ b/sdk/lib/_internal/compiler/implementation/types/type_mask.dart
@@ -59,9 +59,11 @@ class TypeMask {
    * Returns whether or not this type mask contains the given type.
    */
   bool contains(DartType type, Compiler compiler) {
-    // TODO(kasperl): Get rid of this handling.
+    // TODO(kasperl): Do this error handling earlier.
     if (base.isMalformed) return isSubtype;
-    assert(!type.isMalformed);
+    if (base.kind != TypeKind.INTERFACE) return false;
+    assert(type.kind == TypeKind.INTERFACE);
+    // Compare the interface types.
     ClassElement baseElement = base.element;
     ClassElement typeElement = type.element;
     if (isExact) {