TBR js/core: Give extension more time to prepare

This may alleviate the errors in the web tests for namespace browser
and www. Hypothesis: Accessing a page that needs to talk to the extension
too soon, leads to the page failing to initialize the caveat tab.

However, this merely covers up another problem.
https://github.com/vanadium/issues/issues/516

Give extension even more time to get ready

Change-Id: I690739590fbfc1b413a5284cfe02852f309d2419
diff --git a/test/ui/src/test/java/io/v/webdriver/VanadiumUITestBase.java b/test/ui/src/test/java/io/v/webdriver/VanadiumUITestBase.java
index 129bf3e..6c5cee5 100644
--- a/test/ui/src/test/java/io/v/webdriver/VanadiumUITestBase.java
+++ b/test/ui/src/test/java/io/v/webdriver/VanadiumUITestBase.java
@@ -11,6 +11,7 @@
 import org.openqa.selenium.chrome.ChromeDriver;
 import org.openqa.selenium.chrome.ChromeDriverService;
 
+import io.v.webdriver.Util;
 import io.v.webdriver.htmlreport.HTMLReportData;
 import io.v.webdriver.commonpages.ChromeSignInPage;
 import io.v.webdriver.commonpages.ExtensionInstallationPage;
@@ -143,5 +144,8 @@
     // Check Vanadium extension option page.
     ExtensionOptionPage extensionOptionPage = new ExtensionOptionPage(driver, reportData);
     extensionOptionPage.go();
+
+    // Wait a little bit to allow the extension to get ready.
+    Util.sleep(5000);
   }
 }