Remove unused API.

dart/sdk/lib/_internal/compiler/implementation/constants.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 dart2js;
 
 abstract class ConstantVisitor<R> {
   R visitFunction(FunctionConstant constant);
   R visitNull(NullConstant constant);
   R visitInt(IntConstant constant);
@@ skipping 105 matching lines @@
   get value => null;
 
   DartType computeType(Compiler compiler) {
     return compiler.nullClass.computeType(compiler);
   }
 
   ti.TypeMask computeMask(Compiler compiler) {
     return compiler.typesTask.nullType;
   }
 
-  void _writeJsCode(CodeBuffer buffer, ConstantHandler handler) {
-    buffer.write(JsNull);
-  }
-
   // The magic constant has no meaning. It is just a random value.
   int get hashCode => 785965825;
   DartString toDartString() => const LiteralDartString("null");
 
   accept(ConstantVisitor visitor) => visitor.visitNull(this);
 }
 
 abstract class NumConstant extends PrimitiveConstant {
   num get value;
   const NumConstant();
@@ skipping 190 matching lines @@
 
   String toString() {
     return 'StringConstant(${Error.safeToString(value.slowToString())})';
   }
 }
 
 abstract class ObjectConstant extends Constant {
   final DartType type;
 
   ObjectConstant(this.type);
+
   bool isObject() => true;
 
   DartType computeType(Compiler compiler) => type;
 }
 
 class TypeConstant extends ObjectConstant {
   /// The user type that this constant represents.
   final DartType representedType;
 
   TypeConstant(this.representedType, type) : super(type);
@@ skipping 257 matching lines @@
       if (i > 0) sb.write(',');
       sb.write(Error.safeToString(field.name));
       sb.write('=');
       sb.write(Error.safeToString(value));
       i++;
     });
     sb.write('))');
     return sb.toString();
   }
 }