Change dart2js to follow the new spec on the equality operator.

lib/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.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
@@ skipping 2024 matching lines @@
 
 class HEquals extends HRelational {
   HEquals(HStatic target, HInstruction left, HInstruction right)
       : super(target, left, right);
   accept(HVisitor visitor) => visitor.visitEquals(this);
 
   bool get builtin() {
     // All primitive types have === semantics.
     // Note that this includes all constants except the user-constructed
     // objects.
-    return left.isConstantNull() || left.propagatedType.isPrimitive();
+    return left.propagatedType.isPrimitive() ||
+        left.isConstantNull() ||
+        right.isConstantNull();
   }
 
   HType computeTypeFromInputTypes() {
     if (builtin || usesBoolifiedInterceptor) return HType.BOOLEAN;
     return HType.UNKNOWN;
   }
 
   HType computeDesiredTypeForNonTargetInput(HInstruction input) {
     if (input == left && right.propagatedType.isUseful()) {
       // All our useful types have === semantics. But we don't want to
@@ skipping 603 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);
 }