fix more mixin tests to work in strong mode

pkg/dev_compiler/tool/run.js

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This is a utility to run and debug an individual DDC compiled test.
 /// Tests can be run with either node or devtool (a Chrome-based utility with
 /// DOM APIs and developer tools support).
 ///
 /// Install devtool via:
 /// > npm install -g devtool
@@ skipping 35 matching lines @@
 
 function finish(e) {
   if (e) {
     console.log('Test ' + test + ' failed:\n' + e.toString());
     sdk.dart.stackPrint(e);
   } else {
     console.log('Test ' + test + ' passed.');
   }
 }
 
+sdk.dart.ignoreWhitelistedErrors(false);
+sdk.dart.failForWeakModeIsChecks(false);
+sdk._isolate_helper.startRootIsolate(() => {}, []);
+// Make it easier to debug test failures and required for formatter test that
+// assumes custom formatters are enabled.
+sdk._debugger.registerDevtoolsFormatter();
+
 var async_helper = requirejs('async_helper').async_helper;
-sdk._isolate_helper.startRootIsolate(() => {}, []);
 async_helper.asyncTestInitialize(finish);
 
 var module = requirejs(test);
 var lib = test.split('/').slice(-1)[0];
 try {
   var result = module[lib].main();
   // async_helper tests call finish directly - call here for all other
   // tests.
   if (!async_helper.asyncTestStarted) {
     if (!result || !(sdk.async.Future.is(result))) {
       finish();
     } else {
       // Wait iff result is a future
       result.then(sdk.dart.dynamic)(() => finish(), { onError: (e) => finish(e) });
     }
   }
 } catch (e) {
   finish(e);
 }