Add another type JSPositiveInt to show a range analysis in the inferrer would be very beneficial :-…

sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.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 dart2js.js_emitter;
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
  * in classes) are ignored, since they can be treated as non-class elements.
  *
@@ skipping 782 matching lines @@
         unneededClasses.add(interceptor);
       }
     }
 
     // These classes are just helpers for the backend's type system.
     unneededClasses.add(backend.jsMutableArrayClass);
     unneededClasses.add(backend.jsFixedArrayClass);
     unneededClasses.add(backend.jsExtendableArrayClass);
     unneededClasses.add(backend.jsUInt32Class);
     unneededClasses.add(backend.jsUInt31Class);
+    unneededClasses.add(backend.jsPositiveIntClass);
 
     return (ClassElement cls) => !unneededClasses.contains(cls);
   }
 
   void emitFinishClassesInvocationIfNecessary(CodeBuffer buffer) {
     if (needsDefineClass) {
       buffer.write('$finishClassesName($classesCollector,'
                    '$_$isolateProperties,'
                    '${_}null)$N');
 
@@ skipping 786 matching lines @@
   }
 
   bool isDeferred(Element element) {
     return compiler.deferredLoadTask.isDeferred(element);
   }
 
   bool get areAnyElementsDeferred {
     return compiler.deferredLoadTask.areAnyElementsDeferred;
   }
 }