Add most equivalence tests to js_model/model_test

tests/compiler/dart2js/kernel/compile_from_dill_test_helper.dart

 // Copyright (c) 2017, 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.
 
 // Helper to test compilation equivalence between source and .dill based
 // compilation.
 library dart2js.kernel.compile_from_dill_test_helper;
 
 import 'dart:async';
 import 'dart:io';
@@ skipping 168 matching lines @@
         expectIdenticalOutput: test.expectIdenticalOutput);
   }
 }
 
 Future<ResultKind> runTest(
     Uri entryPoint, Map<String, String> memorySourceFiles,
     {bool skipWarnings: false,
     bool skipErrors: false,
     bool verbose: false,
     List<String> options: const <String>[],
+    bool expectAstEquivalence: false,
     bool expectIdenticalOutput: true}) async {
   enableDebugMode();
   EnumCreator.matchKernelRepresentationForTesting = true;
   Elements.usePatchedDart2jsSdkSorting = true;
 
   Directory dir = await Directory.systemTemp.createTemp('dart2js-with-dill');
   print('--- create temp directory $dir -------------------------------');
   memorySourceFiles.forEach((String name, String source) {
     new File.fromUri(dir.uri.resolve(name)).writeAsStringSync(source);
   });
@@ skipping 75 matching lines @@
       elementFilter: elementFilter,
       verbose: verbose);
 
   checkEmitters(compiler1.backend.emitter, compiler2.backend.emitter,
       elementEquivalence: (a, b) => equivalence.entityEquivalence(a, b),
       typeEquivalence: (DartType a, DartType b) {
         return equivalence.typeEquivalence(unalias(a), b);
       },
       verbose: verbose);
 
-  checkGeneratedCode(compiler1.backend, compiler2.backend,
-      elementEquivalence: (a, b) => equivalence.entityEquivalence(a, b));
+  if (expectAstEquivalence) {
+    checkGeneratedCode(compiler1.backend, compiler2.backend,
+        elementEquivalence: (a, b) => equivalence.entityEquivalence(a, b));
+  }
 
   if (expectIdenticalOutput) {
     print('--- checking output------- ---------------------------------------');
     collector1.outputMap
         .forEach((OutputType outputType, Map<String, BufferedOutputSink> map1) {
       if (outputType == OutputType.sourceMap) {
         // TODO(johnniwinther): Support source map from .dill.
         return;
       }
       Map<String, BufferedOutputSink> map2 = collector2.outputMap[outputType];
       checkSets(map1.keys, map2.keys, 'output', equality);
       map1.forEach((String name, BufferedOutputSink output1) {
         BufferedOutputSink output2 = map2[name];
         Expect.stringEquals(output1.text, output2.text);
       });
     });
   }
   return ResultKind.success;
 }