Tighten dart2js typed_data range check

sdk/lib/typed_data/dart2js/native_typed_data_dart2js.dart

Index: sdk/lib/typed_data/dart2js/native_typed_data_dart2js.dart
diff --git a/sdk/lib/typed_data/dart2js/native_typed_data_dart2js.dart b/sdk/lib/typed_data/dart2js/native_typed_data_dart2js.dart
index 17a61b65e77a51285b63a7536b6674c27694aee3..efc4957196584465b59791f1116544c1b9e1514c 100644
--- a/sdk/lib/typed_data/dart2js/native_typed_data_dart2js.dart
+++ b/sdk/lib/typed_data/dart2js/native_typed_data_dart2js.dart
@@ -79,7 +79,8 @@ class NativeTypedData implements TypedData native "ArrayBufferView" {
   }
 
   void _checkIndex(int index, int length) {
-    if (JS('bool', '(# >>> 0 != #)', index, index) || index >= length) {
+    if (JS('bool', '(# >>> 0) !== #', index, index) ||
+        JS('int', '#', index) >= length) {  // 'int' guaranteed by above test.
       _invalidIndex(index, length);
     }
   }