Deal with the JS helper separately from the 'native' keyword.

lib/compiler/implementation/native_handler.dart

Index: lib/compiler/implementation/native_handler.dart
diff --git a/lib/compiler/implementation/native_handler.dart b/lib/compiler/implementation/native_handler.dart
index 68f485aab16fcf76cb7a72ff171cd5760883e832..318d46cdf7b3dfa4152049c59bb340ded9444c38 100644
--- a/lib/compiler/implementation/native_handler.dart
+++ b/lib/compiler/implementation/native_handler.dart
@@ -81,13 +81,8 @@ void maybeEnableNative(Compiler compiler,
           'dart/tests/compiler/dart2js_native')
       || libraryName == 'dart:dom_deprecated'
       || libraryName == 'dart:isolate'
-      || libraryName == 'dart:math'
       || libraryName == 'dart:html') {
     library.canUseNative = true;
-    library.addToScope(compiler.findHelper(const SourceString('JS')), compiler);
-    if (compiler.jsIndexingBehaviorInterface !== null) {
-      library.addToScope(compiler.jsIndexingBehaviorInterface, compiler);
-    }
   }
 }