By pass object boxing for all js primitives.

compiler/lib/implementation/core.js

 // Copyright (c) 2011, 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.
 
 /**
  * Helpers for lazy static initialization.
  */
 var static$uninitialized = {};
 var static$initializing = {};
 
@@ skipping 284 matching lines @@
 }
 
 
 /**
  * These operators need to work correctly with undefined
  * so must be functions.
  */
 function EQ$operator(val1, val2) {
   if (val1 === $Dart$Null) {
     return val2 === $Dart$Null;
-  } else {
-    return (typeof(val1) == 'number' && typeof(val2) == 'number')
-        ? val1 == val2
-        : val1.EQ$operator(val2);
-  }
+  } else if (typeof(val1) == typeof(val2) && typeof val1 != 'object') {
+    // number, boolean, string
+    return val1 === val2;
+  } 
+  return val1.EQ$operator(val2);
 }
 
 function NE$operator(val1, val2) {
   return !EQ$operator(val1, val2);
 }
 
 // The following operator-functions are not called from Dart-generated code, but
 // only from handwritten JS code.
 function INDEX$operator(obj, index) {
   return obj.INDEX$operator(index);
@@ skipping 143 matching lines @@
     return match;
   }
   o.$dartConstId = id;
   $consts[key] = o;
   return o;
 }
 
 function $Dart$MapLiteralFactory() {
   return native__CoreJsUtil__newMapLiteral();
 }