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

sdk/lib/_internal/compiler/implementation/types/flat_type_mask.dart

 // Copyright (c) 2013, 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 types;
 
 /**
  * A flat type mask is a type mask that has been flatten to contain a
  * base type.
  */
@@ skipping 80 matching lines @@
     Backend backend = compiler.backend;
     if (containsOnlyString(compiler)) {
       return cls == compiler.stringClass || cls == backend.stringImplementation;
     }
     if (containsOnlyBool(compiler)) {
       return cls == compiler.boolClass || cls == backend.boolImplementation;
     }
     if (containsOnlyInt(compiler)) {
       return cls == compiler.intClass
           || cls == backend.intImplementation
+          || cls == backend.positiveIntImplementation
           || cls == backend.uint32Implementation
           || cls == backend.uint31Implementation;
     }
     if (containsOnlyDouble(compiler)) {
       return cls == compiler.doubleClass
           || cls == compiler.backend.doubleImplementation;
     }
     return false;
   }
 
@@ skipping 18 matching lines @@
     return satisfies(otherBase, compiler);
   }
 
   bool containsMask(TypeMask other, Compiler compiler) {
     return other.isInMask(this, compiler);
   }
 
   bool containsOnlyInt(Compiler compiler) {
     return base == compiler.intClass
         || base == compiler.backend.intImplementation
+        || base == compiler.backend.positiveIntImplementation
         || base == compiler.backend.uint31Implementation
         || base == compiler.backend.uint32Implementation;
   }
 
   bool containsOnlyDouble(Compiler compiler) {
     return base == compiler.doubleClass
         || base == compiler.backend.doubleImplementation;
   }
 
   bool containsOnlyNum(Compiler compiler) {
@@ skipping 511 matching lines @@
     if (x.isExact) {
       return null;
     } else if (x.isSubclass) {
       return compiler.world.subclassesOf(element);
     } else {
       assert(x.isSubtype);
       return compiler.world.subtypesOf(element);
     }
   }
 }