Disabling alert/popup for Android Webview ChromeClient

I am working on an app which has an activity/fragment that displays web pages for certain sites. Android webview (chrome) is popping up alert dialogs for subscribing to push notifications in some of them, which is causing weird flashing/flickering issue.

This is the section for webview and it's settings

    WebSettings webSettings = webView.getSettings();
    webSettings.setJavaScriptEnabled(true);
    webSettings.setJavaScriptCanOpenWindowsAutomatically(false);
    webSettings.setDomStorageEnabled(true);
    webSettings.setAppCacheEnabled(true);
    webSettings.setAppCacheMaxSize(5 * 1024 * 1024);
    webSettings.setAppCachePath("");
    webSettings.setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);
    webSettings.setUserAgentString(mUserAgent);

    webView.setBackgroundColor(Color.argb(1, 0, 0, 0));
    webView.setWebChromeClient(new WebChromeClient() {

        @Override
        public void onReceivedTitle(WebView view, String title) {
            super.onReceivedTitle(view, title);
            BaseWebViewFragment.this.onReceivedTitle(title);
        }

        @Override
        public void onProgressChanged(WebView view, int newProgress) {
            super.onProgressChanged(view, newProgress);
            progressChanged(view, newProgress);
        }
    });

I need to disable these popups completely but cannot find a way to do it.

I tried disabling JS completely, but it causes loading issue for some of the sites.

I also tried overriding the onJS...() methods for WebChromeClient and canceling/confirming the result but to no avail.

Whats the working approach for this?

from Disabling alert/popup for Android Webview ChromeClient