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

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

Index: sdk/lib/_internal/compiler/implementation/types/types.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/types/types.dart	(revision 30754)
+++ sdk/lib/_internal/compiler/implementation/types/types.dart	(working copy)
@@ -58,6 +58,7 @@
   TypeMask intTypeCache;
   TypeMask uint32TypeCache;
   TypeMask uint31TypeCache;
+  TypeMask positiveIntTypeCache;
   TypeMask doubleTypeCache;
   TypeMask numTypeCache;
   TypeMask boolTypeCache;
@@ -109,6 +110,14 @@
     return uint31TypeCache;
   }
 
+  TypeMask get positiveIntType {
+    if (positiveIntTypeCache == null) {
+      positiveIntTypeCache = new TypeMask.nonNullSubclass(
+          compiler.backend.positiveIntImplementation);
+    }
+    return positiveIntTypeCache;
+  }
+
   TypeMask get doubleType {
     if (doubleTypeCache == null) {
       doubleTypeCache = new TypeMask.nonNullExact(