Fix "extends" checks. Move them out of resolve phase and do them on demand.

frog/type.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class Type extends Element {
   bool isTested = false;
   bool isChecked = false;
 
   /**
    * For core types (int, String, etc) this is the generated type assertion
@@ skipping 91 matching lines @@
   Map<String, Member> getAllMembers() => {};
 
   bool _hasNativeSubtypes;
   bool get hasNativeSubtypes() {
     if (_hasNativeSubtypes == null) {
       _hasNativeSubtypes = subtypes.some((t) => t.isNative);
     }
     return _hasNativeSubtypes;
   }
 
+  void _checkExtends() {
+    var typeParams = genericType.typeParameters;
+    if (typeParams != null && typeArgsInOrder != null) {
+      // TODO(jmesserly): making typeArgsInOrder be a List instead of a
+      // Collection would clean this up.
+      var args = typeArgsInOrder.iterator();
+      var params = typeParams.iterator();
+      while (args.hasNext() && params.hasNext()) {
+        var typeParam = params.next();
+        var typeArg = args.next();
+        if (typeParam.extendsType != null && typeArg != null) {
+          typeArg.ensureSubtypeOf(typeParam.extendsType, typeParam.span, true);
+        }
+      }
+    }
+
+    // Parent should be handled by the super constructor call, but we still
+    // need to check our interfaces.
+    if (interfaces != null) {
+      for (var i in interfaces) {
+        i._checkExtends();
+      }
+    }
+  }
+
   void _checkOverride(Member member) {
     // always look in parents to check that any overloads are legal
     var parentMember = _getMemberInParents(member.name);
     if (parentMember != null) {
       // TODO(jimhug): Ensure that this is only done once.
       if (!member.isPrivate || member.library == parentMember.library) {
         member.override(parentMember);
       }
     }
   }
@@ skipping 396 matching lines @@
 
 /** A concrete version of a generic type. */
 class ConcreteType extends Type {
   final DefinedType genericType;
   Map<String, Type> typeArguments;
   List<Type> _interfaces;
   Type _parent;
   Set<Type> _subtypes;
   List<Type> typeArgsInOrder;