[ChromeDriver] Add alert text to UnexpectedAlert status

Add the text of the open alert when returning UnexpectedAlertOpen.

Bug: chromedriver:3184
Change-Id: Ifcd0e59c0d5d32089fca20b01b6f626ea5b4e741
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1898385Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Tricia Crichton <triciac@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712617}

chrome/test/chromedriver/chrome/web_view_impl.cc

@@ -1113,8 +1113,13 @@ Status WebViewImpl::IsNotPendingNavigation(const std::string& frame_id,
   if (status.IsError())
     return status;
   // An alert may block the pending navigation.
-  if (dialog_manager_->IsDialogOpen())
+  if (dialog_manager_->IsDialogOpen()) {
+    std::string alert_text;
+    status = dialog_manager_->GetDialogMessage(&alert_text);
+    if (status.IsError())
       return Status(kUnexpectedAlertOpen);
+    return Status(kUnexpectedAlertOpen, "{Alert text : " + alert_text + "}");
+  }
 
   *is_not_pending = !is_pending;
   return Status(kOk);