Reapply change to update dart2js operator equals semantics to follow

lib/compiler/implementation/ssa/optimize.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 OptimizationPhase {
   String get name();
   void visitGraph(HGraph graph);
 }
 
 class SsaOptimizerTask extends CompilerTask {
@@ skipping 442 matching lines @@
       } else {
         // We can just emit an identity check because the type does
         // not implement operator=.
         return foldBuiltinEqualsCheck(node);
       }
     }
 
     if (right.isConstantNull()) {
       if (left.propagatedType.isPrimitive()) {
         return graph.addConstantBool(false);
-      } else {
-        // TODO(floitsch): cache interceptors.
-        Interceptors interceptors = backend.builder.interceptors;
-        Element equalsElement = interceptors.getEqualsInterceptor();
-        // If we have a different element than [equalsElement], we
-        // don't need to optimize this instruction to use another
-        // element: we know the element is either eqNull or eqNullB.
-        if (node.element === equalsElement) {
-          Element targetElement = interceptors.getEqualsNullInterceptor();
-          bool onlyUsedInBoolify = allUsersAreBoolifies(node);
-          if (onlyUsedInBoolify) {
-            targetElement = interceptors.getBoolifiedVersionOf(targetElement);
-          }
-          HStatic target = new HStatic(targetElement);
-          node.block.addBefore(node, target);
-          HEquals result = new HEquals(target, node.left, node.right);
-          if (onlyUsedInBoolify) {
-            result.usesBoolifiedInterceptor = true;
-            result.propagatedType = HType.BOOLEAN;
-          }
-          return result;
-        }
       }
     }
 
     // All other cases are dealt with by the [visitRelational] and
     // [visitInvokeBinary], which are visited by invoking the [super]'s
     // visit method.
     return super.visitEquals(node);
   }
 
   HInstruction visitTypeGuard(HTypeGuard node) {
@@ skipping 772 matching lines @@
             break;
           default:
             assert(false);
             break;
         }
       }
     }
   }
 
 }