Revert "Add native_testing library to mock @Native classes"

sdk/lib/_internal/js_runtime/lib/native_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/native_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/native_helper.dart b/sdk/lib/_internal/js_runtime/lib/native_helper.dart
index c6aad9430c4302c697a8244b7b667d39de0029fd..30d3ba7458745ee64f0a0888b47e10f3c32f51ff 100644
--- a/sdk/lib/_internal/js_runtime/lib/native_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/native_helper.dart
@@ -449,9 +449,13 @@ applyHooksTransformer(transformer, hooks) {
 
 const _baseHooks = const JS_CONST(r'''
 function() {
-  var toStringFunction = Object.prototype.toString;
-  function getTag(o) {
-    var s = toStringFunction.call(o);
+  function typeNameInChrome(o) {
+    var constructor = o.constructor;
+    if (constructor) {
+      var name = constructor.name;
+      if (name) return name;
+    }
+    var s = Object.prototype.toString.call(o);
     return s.substring(8, s.length - 1);
   }
   function getUnknownTag(object, tag) {
@@ -459,7 +463,7 @@ function() {
     // here allows [getUnknownTag] to be tested on d8.
     if (/^HTML[A-Z].*Element$/.test(tag)) {
       // Check that it is not a simple JavaScript object.
-      var name = toStringFunction.call(object);
+      var name = Object.prototype.toString.call(object);
       if (name == "[object Object]") return null;
       return "HTMLElement";
     }
@@ -480,7 +484,7 @@ function() {
   var isBrowser = typeof navigator == "object";
 
   return {
-    getTag: getTag,
+    getTag: typeNameInChrome,
     getUnknownTag: isBrowser ? getUnknownTagGenericBrowser : getUnknownTag,
     prototypeForTag: prototypeForTag,
     discriminator: discriminator };