Reapply change to update dart2js operator equals semantics to follow

lib/compiler/implementation/ssa/codegen.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.
 
 class SsaCodeGeneratorTask extends CompilerTask {
   final JavaScriptBackend backend;
   SsaCodeGeneratorTask(JavaScriptBackend backend)
       : this.backend = backend,
         super(backend.compiler);
   String get name() => 'SSA code generator';
@@ skipping 223 matching lines @@
                    this.parameters,
                    this.parameterNames)
     : declaredVariables = new Set<String>(),
       delayedVariableDeclarations = new Set<String>(),
       buffer = new StringBuffer(),
       generateAtUseSite = new Set<HInstruction>(),
       controlFlowOperators = new Set<HInstruction>(),
       breakAction = new Map<Element, ElementAction>(),
       continueAction = new Map<Element, ElementAction>(),
       unsignedShiftPrecedences = JSPrecedence.binary['>>>'] {
-
-    Interceptors interceptors = backend.builder.interceptors;
-    equalsNullElement = interceptors.getEqualsNullInterceptor();
-    boolifiedEqualsNullElement =
-        interceptors.getBoolifiedVersionOf(equalsNullElement);
   }
 
   abstract visitTypeGuard(HTypeGuard node);
 
   abstract beginGraph(HGraph graph);
   abstract endGraph(HGraph graph);
 
   abstract beginLoop(HBasicBlock block);
   abstract endLoop(HBasicBlock block);
   abstract handleLoopCondition(HLoopBranch node);
@@ skipping 999 matching lines @@
       use(left, JSPrecedence.EQUALITY_PRECEDENCE);
       buffer.add(' === ');
       use(right, JSPrecedence.RELATIONAL_PRECEDENCE);
       endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
     }
   }
 
   visitEquals(HEquals node) {
     if (node.builtin) {
       emitIdentityComparison(node.left, node.right);
-    } else if (node.element === equalsNullElement ||
-               node.element === boolifiedEqualsNullElement) {
-      beginExpression(JSPrecedence.CALL_PRECEDENCE);
-      use(node.target, JSPrecedence.CALL_PRECEDENCE);
-      buffer.add('(');
-      use(node.left, JSPrecedence.ASSIGNMENT_PRECEDENCE);
-      buffer.add(')');
-      endExpression(JSPrecedence.CALL_PRECEDENCE);
     } else {
       visitInvokeStatic(node);
     }
   }
 
   visitIdentity(HIdentity node) {
     assert(node.builtin);
     emitIdentityComparison(node.left, node.right);
   }
 
@@ skipping 1817 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endLabeledBlock(HLabeledBlockInformation labeledBlockInfo) {
     if (labeledBlockInfo.body.start.hasGuards()) {
       endBailoutSwitch();
     }
   }
 }