Fix braino: iteration is through a loop, so you continue it with continue.

lib/compiler/implementation/js_backend/native_emitter.dart

Index: lib/compiler/implementation/js_backend/native_emitter.dart
===================================================================
--- lib/compiler/implementation/js_backend/native_emitter.dart	(revision 12913)
+++ lib/compiler/implementation/js_backend/native_emitter.dart	(working copy)
@@ -397,7 +397,7 @@
   void emitIsChecks(Map<String, String> objectProperties) {
     for (Element element in emitter.checkedClasses) {
       if (!requiresNativeIsCheck(element)) continue;
-      if (element.isObject(compiler)) return;
+      if (element.isObject(compiler)) continue;
       String name = backend.namer.operatorIs(element);
       objectProperties[name] = 'function() { return false; }';
     }