dart2js: Don't emit nsm handlers if nobody needs them in the new emitter.

pkg/compiler/lib/src/js_emitter/program_builder.dart

Index: pkg/compiler/lib/src/js_emitter/program_builder.dart
diff --git a/pkg/compiler/lib/src/js_emitter/program_builder.dart b/pkg/compiler/lib/src/js_emitter/program_builder.dart
index 2d22ead02315ee95bb458efb7d9fb5dbc76f3817..29d9ed015e6510b416322d8a9a6447ca3404e684 100644
--- a/pkg/compiler/lib/src/js_emitter/program_builder.dart
+++ b/pkg/compiler/lib/src/js_emitter/program_builder.dart
@@ -356,7 +356,7 @@ class ProgramBuilder {
         runtimeTypeGenerator.generateTypeVariableReaderStubs(element);
 
     List<StubMethod> noSuchMethodStubs = <StubMethod>[];
-    if (element == _compiler.objectClass) {
+    if (_compiler.enabledNoSuchMethod && element == _compiler.objectClass) {
       Map<String, Selector> selectors =
           classStubGenerator.computeSelectorsForNsmHandlers();
       selectors.forEach((String name, Selector selector) {