Implement is-checks with typedefs for callable objects.

sdk/lib/_internal/compiler/implementation/ssa/nodes.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 ssa;
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
@@ skipping 2523 matching lines @@
                          [this.nullOk = false])
     : super(<HInstruction>[expression]..addAll(checks));
 
   HIs(this.typeExpression, HInstruction expression, {this.nullOk: false})
      : super(<HInstruction>[expression]);
 
   HInstruction get expression => inputs[0];
   HInstruction getCheck(int index) => inputs[index + 1];
   int get checkCount => inputs.length - 1;
 
-  bool hasArgumentChecks() => inputs.length >= 1;
+  bool hasArgumentChecks() => inputs.length > 1;
 
   HType get guaranteedType => HType.BOOLEAN;
 
   accept(HVisitor visitor) => visitor.visitIs(this);
 
   toString() => "$expression is $typeExpression";
 }
 
 class HTypeConversion extends HCheck {
   HType type;
@@ skipping 387 matching lines @@
   HBasicBlock get start => expression.start;
   HBasicBlock get end {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty);
     return statements.last.end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }