Fix analyzer warnings in assertions of the TypeExpression CL

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

 // Copyright (c) 2014, 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.
 
 library code_generator;
 
 import 'glue.dart';
 
 import '../../closure.dart' show
     ClosureClassElement;
@@ skipping 974 matching lines @@
 
   @override
   js.Expression visitTypeExpression(tree_ir.TypeExpression node) {
     List<js.Expression> arguments = visitExpressionList(node.arguments);
     switch (node.kind) {
       case tree_ir.TypeExpressionKind.COMPLETE:
         return glue.generateTypeRepresentation(
             node.dartType, arguments, registry);
       case tree_ir.TypeExpressionKind.INSTANCE:
         // We expect only flat types for the INSTANCE representation.
-        assert(node.dartType == node.dartType.element.thisType);
+        assert(node.dartType ==
+               (node.dartType.element as ClassElement).thisType);
         registry.registerInstantiatedClass(glue.listClass);
         return new js.ArrayInitializer(arguments);
     }
   }
 
   js.Node handleForeignCode(tree_ir.ForeignCode node) {
     if (node.dependency != null) {
       // Dependency is only used if [node] calls a Dart function. Currently only
       // through foreign function `RAW_DART_FUNCTION_REF`.
       registry.registerStaticUse(
@@ skipping 227 matching lines @@
   void registerDefaultParameterValues(ExecutableElement element) {
     if (element is! FunctionElement) return;
     FunctionElement function = element;
     if (function.isStatic) return; // Defaults are inlined at call sites.
     function.functionSignature.forEachOptionalParameter((param) {
       ConstantValue constant = glue.getDefaultParameterValue(param);
       registry.registerCompileTimeConstant(constant);
     });
   }
 }