dart2js: Move lowering of identical(a, b) from builder to optimizer

pkg/compiler/lib/src/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.
 
 import '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
 import '../common/names.dart' show Selectors;
 import '../common/tasks.dart' show CompilerTask;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
@@ skipping 987 matching lines @@
         value = other;
       }
     }
     return new HFieldSet(field, receiver, value);
   }
 
   HInstruction visitInvokeStatic(HInvokeStatic node) {
     propagateConstantValueToUses(node);
     MemberEntity element = node.element;
 
-    if (element == backend.helpers.checkConcurrentModificationError) {
+    if (element == compiler.commonElements.identicalFunction) {
+      if (node.inputs.length == 2) {
+        return new HIdentity(node.inputs[0], node.inputs[1], null,
+            closedWorld.commonMasks.boolType)
+          ..sourceInformation = node.sourceInformation;
+      }
+    } else if (element == backend.helpers.checkConcurrentModificationError) {
       if (node.inputs.length == 2) {
         HInstruction firstArgument = node.inputs[0];
         if (firstArgument is HConstant) {
           HConstant constant = firstArgument;
           if (constant.constant.isTrue) return constant;
         }
       }
     } else if (element == backend.helpers.checkInt) {
       if (node.inputs.length == 1) {
         HInstruction argument = node.inputs[0];
@@ skipping 1735 matching lines @@
 
     keyedValues.forEach((receiver, values) {
       result.keyedValues[receiver] =
           new Map<HInstruction, HInstruction>.from(values);
     });
 
     result.nonEscapingReceivers.addAll(nonEscapingReceivers);
     return result;
   }
 }