Convert a == to a builtin identity check if the receiver type can only hit Object==.

sdk/lib/_internal/compiler/implementation/js_backend/backend.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.
 
 part of js_backend;
 
 typedef void Recompile(Element element);
 
 class ReturnInfo {
   HType returnType;
@@ skipping 637 matching lines @@
   ClassElement jsFixedArrayClass;
   ClassElement jsExtendableArrayClass;
 
   Element jsArrayLength;
   Element jsStringLength;
   Element jsArrayRemoveLast;
   Element jsArrayAdd;
   Element jsStringSplit;
   Element jsStringConcat;
   Element jsStringToString;
+  Element objectEquals;
 
   ClassElement typeLiteralClass;
   ClassElement mapLiteralClass;
   ClassElement constMapLiteralClass;
 
   Element getInterceptorMethod;
   Element interceptedNames;
 
   bool seenAnyClass = false;
 
@@ skipping 222 matching lines @@
     for (ClassElement cls in classes) {
       if (cls != null) interceptedClasses.add(cls);
     }
 
     typeLiteralClass = compiler.findHelper(const SourceString('TypeImpl'));
     mapLiteralClass =
         compiler.coreLibrary.find(const SourceString('LinkedHashMap'));
     constMapLiteralClass =
         compiler.findHelper(const SourceString('ConstantMap'));
 
+    objectEquals = compiler.lookupElementIn(
+        compiler.objectClass, const SourceString('=='));
+
     specialOperatorEqClasses
         ..add(jsNullClass)
         ..add(jsNumberClass);
   }
 
   void addInterceptorsForNativeClassMembers(
       ClassElement cls, Enqueuer enqueuer) {
     if (enqueuer.isResolutionQueue) {
       cls.ensureResolved(compiler);
       cls.forEachMember((ClassElement classElement, Element member) {
@@ skipping 753 matching lines @@
   ClassElement get constListImplementation => jsArrayClass;
   ClassElement get fixedListImplementation => jsFixedArrayClass;
   ClassElement get growableListImplementation => jsExtendableArrayClass;
   ClassElement get mapImplementation => mapLiteralClass;
   ClassElement get constMapImplementation => constMapLiteralClass;
   ClassElement get functionImplementation => jsFunctionClass;
   ClassElement get typeImplementation => typeLiteralClass;
   ClassElement get boolImplementation => jsBoolClass;
   ClassElement get nullImplementation => jsNullClass;
 }