[ios] Use new JS execution API in browsing data partitioning test.

ios/web/public/test/js_test_util.h

Index: ios/web/public/test/js_test_util.h
diff --git a/ios/web/public/test/js_test_util.h b/ios/web/public/test/js_test_util.h
index 2cc2c1e7b8db02f088c55f779f87a77a17230621..ea21a5098a0ed6ab97ea5962312a2a35438af346 100644
--- a/ios/web/public/test/js_test_util.h
+++ b/ios/web/public/test/js_test_util.h
@@ -26,6 +26,11 @@ id ExecuteJavaScript(CRWJSInjectionManager* manager, NSString* script);
 id ExecuteJavaScript(CRWJSInjectionReceiver* receiver, NSString* script);
 
 // Executes JavaScript on |web_view| and returns the result as an id.
+// |error| can be null and will be updated only if script execution fails.
+id ExecuteJavaScript(WKWebView* web_view, NSString* script, NSError** error);
+
+// Executes JavaScript on |web_view| and returns the result as an id.
+// Fails if there was an error during script execution.
 id ExecuteJavaScript(WKWebView* web_view, NSString* script);
 
 }  // namespace web