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

sdk/lib/typed_data/dart2js/typed_data_dart2js.dart

Index: sdk/lib/typed_data/dart2js/typed_data_dart2js.dart
===================================================================
--- sdk/lib/typed_data/dart2js/typed_data_dart2js.dart	(revision 30705)
+++ sdk/lib/typed_data/dart2js/typed_data_dart2js.dart	(working copy)
@@ -10,7 +10,7 @@
 
 import 'dart:collection';
 import 'dart:_collection-dev';
-import 'dart:_interceptors' show JSIndexable;
+import 'dart:_interceptors' show JSIndexable, JSUInt32, JSUInt31;
 import 'dart:_js_helper'
     show Creates, JavaScriptIndexingBehavior, JSName, Null, Returns;
 import 'dart:_foreign_helper' show JS, JS_CONST;
@@ -259,7 +259,7 @@
       _getUint16(byteOffset, endian._littleEndian);
 
   @JSName('getUint16')
-  @Returns('int')
+  @Returns('JSUInt31')
   int _getUint16(int byteOffset, [bool littleEndian]) native;
 
   /**
@@ -275,7 +275,7 @@
       _getUint32(byteOffset, endian._littleEndian);
 
   @JSName('getUint32')
-  @Returns('int')
+  @Returns('JSUInt32')
   int _getUint32(int byteOffset, [bool littleEndian]) native;
 
   /**
@@ -874,7 +874,7 @@
 
   int operator[](int index) {
     _checkIndex(index, length);
-    return JS("int", "#[#]", this, index);
+    return JS("JSUInt31", "#[#]", this, index);
   }
 
   void operator[]=(int index, int value) {
@@ -948,7 +948,7 @@
 
   int operator[](int index) {
     _checkIndex(index, length);
-    return JS("int", "#[#]", this, index);
+    return JS("JSUInt32", "#[#]", this, index);
   }
 
   void operator[]=(int index, int value) {
@@ -1019,7 +1019,7 @@
 
   int operator[](int index) {
     _checkIndex(index, length);
-    return JS("int", "#[#]", this, index);
+    return JS("JSUInt31", "#[#]", this, index);
   }
 
   void operator[]=(int index, int value) {
@@ -1095,7 +1095,7 @@
 
   int operator[](int index) {
     _checkIndex(index, length);
-    return JS("int", "#[#]", this, index);
+    return JS("JSUInt31", "#[#]", this, index);
   }
 
   void operator[]=(int index, int value) {
@@ -1364,7 +1364,8 @@
   }
 
   void _checkIndex(int index, int length) {
-    if (JS('bool', '(# >>> 0 != #)', index, index) || index >= length) {
+    if (JS('bool', '(# >>> 0 != #)', index, index)
+        || JS('bool', '# >= #', index, length)) {
       _invalidIndex(index, length);
     }
   }