Add most equivalence tests to js_model/model_test

tests/compiler/dart2js/kernel/compile_from_dill_test_helper.dart

Index: tests/compiler/dart2js/kernel/compile_from_dill_test_helper.dart
diff --git a/tests/compiler/dart2js/kernel/compile_from_dill_test_helper.dart b/tests/compiler/dart2js/kernel/compile_from_dill_test_helper.dart
index 3910002ea3034cdc1fc48ad20a4e4d2b0b1b1b08..28ecc4519404a24300dff5e9c1d06054ac5e08a1 100644
--- a/tests/compiler/dart2js/kernel/compile_from_dill_test_helper.dart
+++ b/tests/compiler/dart2js/kernel/compile_from_dill_test_helper.dart
@@ -186,6 +186,7 @@ Future<ResultKind> runTest(
     bool skipErrors: false,
     bool verbose: false,
     List<String> options: const <String>[],
+    bool expectAstEquivalence: false,
     bool expectIdenticalOutput: true}) async {
   enableDebugMode();
   EnumCreator.matchKernelRepresentationForTesting = true;
@@ -281,8 +282,10 @@ Future<ResultKind> runTest(
       },
       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------- ---------------------------------------');