Fix compilation errors

pkg/analyzer/lib/src/task/strong/checker.dart

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this was ported from package:dev_compiler, and needs to be
 // refactored to fit into analyzer.
 library analyzer.src.task.strong.checker;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 825 matching lines @@
     var type = functionType.returnType;
 
     InterfaceType expectedType = null;
     if (body.isAsynchronous) {
       if (body.isGenerator) {
         // Stream<T> -> T
         expectedType = typeProvider.streamType;
       } else {
         // Future<T> -> FutureOr<T>
         var typeArg = (type.element == typeProvider.futureType.element)
-            ? type.typeArguments[0]
+            ? (type as InterfaceType).typeArguments[0]
             : typeProvider.dynamicType;
         return typeProvider.futureOrType.instantiate([typeArg]);
       }
     } else {
       if (body.isGenerator) {
         // Iterable<T> -> T
         expectedType = typeProvider.iterableType;
       } else {
         // T -> T
         return type;
@@ skipping 66 matching lines @@
 
     // fromT <: toT, no coercion needed.
     if (rules.isSubtypeOf(from, to)) return false;
 
     // Down cast or legal sideways cast, coercion needed.
     if (rules.isAssignableTo(from, to)) return true;
 
     // Special case for FutureOr to handle returned values from async functions.
     // In this case, we're more permissive than assignability.
     if (to.element == typeProvider.futureOrType.element) {
-      var to1 = to.typeArguments[0];
+      var to1 = (to as InterfaceType).typeArguments[0];
       var to2 = typeProvider.futureType.instantiate([to1]);
       return _needsImplicitCast(expr, to1, from: from) == true ||
           _needsImplicitCast(expr, to2, from: from) == true;
     }
 
     // Anything else is an illegal sideways cast.
     // However, these will have been reported already in error_verifier, so we
     // don't need to report them again.
     return null;
   }
@@ skipping 620 matching lines @@
     var visited = new Set<InterfaceType>();
     do {
       visited.add(current);
       current.mixins.reversed.forEach(
           (m) => _checkIndividualOverridesFromClass(node, m, seen, true));
       _checkIndividualOverridesFromClass(node, current.superclass, seen, true);
       current = current.superclass;
     } while (!current.isObject && !visited.contains(current));
   }
 }