url: do not define @@toStringTag with a getter

lib/internal/url.js

@@ -221,10 +221,11 @@ class URL {
     if (base !== undefined && !(base instanceof URL))
       base = new URL(String(base));
     parse(this, input, base);
-  }
 
-  get [Symbol.toStringTag]() {
-    return this instanceof URL ? 'URL' : 'URLPrototype';
+    Object.defineProperty(this, Symbol.toStringTag, {
+      configurable: true,
+      value: 'URL'
+    });
   }
 
   get [special]() {
@@ -314,6 +315,10 @@ Object.defineProperties(URL.prototype, {
       return ret;
     }
   },
+  [Symbol.toStringTag]: {
+    configurable: true,
+    value: 'URLPrototype'
+  },
   href: {
     enumerable: true,
     configurable: true,

test/parallel/test-whatwg-url-properties.js

@@ -45,7 +45,7 @@ assert.strictEqual(url.searchParams, oldParams);  // [SameObject]
 // Note: this error message is subject to change in V8 updates
 assert.throws(() => url.origin = 'http://foo.bar.com:22',
               new RegExp('TypeError: Cannot set property origin of' +
-                         ' \\[object Object\\] which has only a getter'));
+                         ' \\[object URLPrototype\\] which has only a getter'));
 assert.strictEqual(url.origin, 'http://foo.bar.com:21');
 assert.strictEqual(url.toString(),
                    'http://user:[email protected]:21/aaa/zzz?l=25#test');
@@ -121,7 +121,7 @@ assert.strictEqual(url.hash, '#abcd');
 // Note: this error message is subject to change in V8 updates
 assert.throws(() => url.searchParams = '?k=88',
               new RegExp('TypeError: Cannot set property searchParams of' +
-                         ' \\[object Object\\] which has only a getter'));
+                         ' \\[object URLPrototype\\] which has only a getter'));
 assert.strictEqual(url.searchParams, oldParams);
 assert.strictEqual(url.toString(),
                    'https://user2:[email protected]:23/aaa/bbb?k=99#abcd');