Fix checked mode error.

tests/language/issue10204_test.dart

 // Copyright (c) 2013, 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.
 
 // Regression test for dart2js that used to miscompile
 // [A.visitInvokeDynamicMethod].
 
 import "package:expect/expect.dart";
 
 var a = 2;
 
 class Tupe {
   const Tupe();
   get instructionType => a == 2 ? this : new A();
   refine(a, b) => '$a$b';
 }
 
 class Node {
   final selector = null;
   var inputs = {"a": const Tupe(), "b": const Tupe() };
-  bool isCallOnInterceptor;
+  bool isCallOnInterceptor = false;
 
   getDartReceiver() {
     return isCallOnInterceptor ? inputs["a"] : inputs["b"];
   }
 }
 
 class A {
   visitInvokeDynamicMethod(node) {
     var receiverType = node.getDartReceiver().instructionType;
     return receiverType.refine(node.selector, node.selector);
   }
 }
 
 main() {
   Expect.equals('nullnull',
                 [new A()].last.visitInvokeDynamicMethod(new Node()));
 }