[ServiceWorker] Fix bugs of wpt tests for Client.navigate

third_party/WebKit/LayoutTests/resources/testharness.js

Index: third_party/WebKit/LayoutTests/resources/testharness.js
diff --git a/third_party/WebKit/LayoutTests/resources/testharness.js b/third_party/WebKit/LayoutTests/resources/testharness.js
index bb63e02caf72d48b6151ccfd24f68c24598f0d08..0e6f7608c0f8f6860a6a9a0d880e376158322d5f 100644
--- a/third_party/WebKit/LayoutTests/resources/testharness.js
+++ b/third_party/WebKit/LayoutTests/resources/testharness.js
@@ -483,7 +483,10 @@ policies and contribution forms [3].
     }
 
     function is_service_worker(worker) {
-        return 'ServiceWorker' in self && worker instanceof ServiceWorker;
+        // The worker object may be from another execution context,
+        // so do not use instanceof here.
+        return 'ServiceWorker' in self &&
+            Object.prototype.toString.call(worker) == '[object ServiceWorker]';
     }
 
     /*