PlzNavigate: fix timing issue in app window creation

content/test/web_contents_observer_sanity_checker.cc

Index: content/test/web_contents_observer_sanity_checker.cc
diff --git a/content/test/web_contents_observer_sanity_checker.cc b/content/test/web_contents_observer_sanity_checker.cc
index 09151e89135750a398e7a6b909227f4418abb1ed..82bcb60461840a005453f0d271ce50cd3de1e7bd 100644
--- a/content/test/web_contents_observer_sanity_checker.cc
+++ b/content/test/web_contents_observer_sanity_checker.cc
@@ -143,6 +143,15 @@ void WebContentsObserverSanityChecker::DidRedirectNavigation(
   CHECK(!navigation_handle->HasCommittedErrorPage());
 }
 
+void WebContentsObserverSanityChecker::ReadyToCommitNavigation(
+    NavigationHandle* navigation_handle) {
+  CHECK(NavigationIsOngoing(navigation_handle));
+  CHECK(!NavigationIsOngoingAndCommitted(navigation_handle));
+
+  CHECK(!navigation_handle->HasCommittedDocument());
+  CHECK(!navigation_handle->HasCommittedErrorPage());
+}
+
 void WebContentsObserverSanityChecker::DidCommitNavigation(
     NavigationHandle* navigation_handle) {
   CHECK(NavigationIsOngoing(navigation_handle));