Fix evaluation of !=

pkg/compiler/lib/src/constants/expressions.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 dart2js.constants.expressions;
 
 import '../common.dart';
 import '../constants/constant_system.dart';
 import '../core_types.dart';
 import '../dart_types.dart';
@@ skipping 852 matching lines @@
     sb.write('Binary(left=');
     left._createStructuredText(sb);
     sb.write(',op=$operator,right=');
     right._createStructuredText(sb);
     sb.write(')');
   }
 
   @override
   ConstantValue evaluate(
       Environment environment, ConstantSystem constantSystem) {
-    return constantSystem.lookupBinary(operator).fold(
-        left.evaluate(environment, constantSystem),
-        right.evaluate(environment, constantSystem));
+    ConstantValue leftValue = left.evaluate(environment, constantSystem);
+    ConstantValue rightValue = right.evaluate(environment, constantSystem);
+    switch (operator.kind) {
+      case BinaryOperatorKind.NOT_EQ:
+        BoolConstantValue equals =
+            constantSystem.equal.fold(leftValue, rightValue);
+        return equals.negate();
+      default:
+        return constantSystem
+            .lookupBinary(operator)
+            .fold(leftValue, rightValue);
+    }
   }
 
   ConstantExpression apply(NormalizedArguments arguments) {
     return new BinaryConstantExpression(
         left.apply(arguments), operator, right.apply(arguments));
   }
 
   DartType getKnownType(CoreTypes coreTypes) {
     DartType knownLeftType = left.getKnownType(coreTypes);
     DartType knownRightType = right.getKnownType(coreTypes);
@@ skipping 987 matching lines @@
     visit(exp.name);
     if (exp.defaultValue != null) {
       sb.write(', defaultValue: ');
       visit(exp.defaultValue);
     }
     sb.write(')');
   }
 
   String toString() => sb.toString();
 }