Use typedefs in lib.

sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

 // Copyright (c) 2012, 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.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 1525 matching lines @@
     String receiver = backend.isInterceptorClass(member.getEnclosingClass())
         ? 'receiver' : 'this';
     List<String> args = backend.isInterceptedMethod(member)
         ? ['receiver', 'v']
         : ['v'];
     builder.addProperty(setterName,
         js.fun(args, js('$receiver.$fieldName = v')));
   }
 
   bool canGenerateCheckedSetter(Element member) {
-    DartType type = member.computeType(compiler);
-    if (type.element.isTypeVariable()
-        || type.element == compiler.dynamicClass
-        || type.element == compiler.objectClass) {
+    DartType type = member.computeType(compiler).unalias(compiler);
+    if (type.element.isTypeVariable() ||
+        (type is FunctionType && type.containsTypeVariables) || 
+        type.element == compiler.dynamicClass ||
+        type.element == compiler.objectClass) {
       // TODO(ngeoffray): Support type checks on type parameters.
       return false;
     }
     return true;
   }
 
   void generateCheckedSetter(Element member,
                              String fieldName,
                              String accessorName,
                              ClassBuilder builder) {
     assert(canGenerateCheckedSetter(member));
     DartType type = member.computeType(compiler);
     // TODO(ahe): Generate a dynamic type error here.
     if (type.element.isErroneous()) return;
     type = type.unalias(compiler);
+    // TODO(11273): Support complex subtype checks.
+    type = type.asRaw();
     CheckedModeHelper helper =
         backend.getCheckedModeHelper(type, typeCast: false);
     FunctionElement helperElement = helper.getElement(compiler);
     String helperName = namer.isolateAccess(helperElement);
     List<jsAst.Expression> arguments = <jsAst.Expression>[js('v')];
     if (helperElement.computeSignature(compiler).parameterCount != 1) {
       arguments.add(js.string(namer.operatorIsType(type)));
     }
 
     String setterName = namer.setterNameFromAccessorName(accessorName);
@@ skipping 2126 matching lines @@
 
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;