Revert "Add native_testing library to mock @Native classes"

sdk/lib/_internal/js_runtime/lib/interceptors.dart

Index: sdk/lib/_internal/js_runtime/lib/interceptors.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/interceptors.dart b/sdk/lib/_internal/js_runtime/lib/interceptors.dart
index f13c3f8f4200f300fd51e1f9d8b9131a3f6cace1..23025ad578cc34276949080428a92a0e7b49fcab 100644
--- a/sdk/lib/_internal/js_runtime/lib/interceptors.dart
+++ b/sdk/lib/_internal/js_runtime/lib/interceptors.dart
@@ -168,16 +168,7 @@ getNativeInterceptor(object) {
     }
   }
 
-  // Check for cached UnknownJavaScriptObject. This avoids doing the slow
-  // dispatch-record based lookup for repeated js-interop classes.
-  var constructor = JS('', '#.constructor', object);
-  var interceptor = JS('', '#.get(#)', constructorToInterceptor, constructor);
-  if (interceptor != null) return interceptor;
-
-  // This takes care of dispatch-record based caching, but not constructor based
-  // caching of [UnknownJavaScriptObject]s.
-  interceptor = lookupAndCacheInterceptor(object);
-
+  var interceptor = lookupAndCacheInterceptor(object);
   if (interceptor == null) {
     // JavaScript Objects created via object literals and `Object.create(null)`
     // are 'plain' Objects.  This test could be simplified and the dispatch path
@@ -189,10 +180,6 @@ getNativeInterceptor(object) {
     var proto = JS('', 'Object.getPrototypeOf(#)', object);
     if (JS('bool', '# == null || # === Object.prototype', proto, proto)) {
       return JS_INTERCEPTOR_CONSTANT(PlainJavaScriptObject);
-    } else if (JS('bool', 'typeof # == "function"', constructor)) {
-      interceptor = JS_INTERCEPTOR_CONSTANT(UnknownJavaScriptObject);
-      JS('', '#.set(#, #)', constructorToInterceptor, constructor, interceptor);
-      return interceptor;
     } else {
       return JS_INTERCEPTOR_CONSTANT(UnknownJavaScriptObject);
     }
@@ -201,9 +188,6 @@ getNativeInterceptor(object) {
   return interceptor;
 }
 
-var constructorToInterceptor =
-    JS('', 'typeof(self.WeakMap) == "undefined" ? new Map() : new WeakMap()');
-
 /**
  * Data structure used to map a [Type] to the [Interceptor] and constructors for
  * that type.  It is JavaScript array of 3N entries of adjacent slots containing