enable system webview debug and append js flags to system webview, works on Pixel3, enjoy!

enable_webview_debug_js_flags.js

Java.perform(function() {
    var Webview = Java.use("android.webkit.WebView")
    Webview.loadUrl.overload("java.lang.String").implementation = function(url) {
        console.log("[+]Loading URL from", url);
        this.setWebContentsDebuggingEnabled(true);
        this.loadUrl.overload("java.lang.String").call(this, url);
    }
});

// var dlopen_addr = Module.findExportByName(null, 'dlopen');
var android_dlopen_ext_addr = Module.findExportByName(null, 'android_dlopen_ext');

if(android_dlopen_ext_addr){
    Interceptor.attach(android_dlopen_ext_addr, function (args) {
        if(args[0].readCString().endsWith('libmonochrome.so')){
            console.log("[+]I see you....");
            Java.perform(function () {
                Java.enumerateClassLoaders({
                    onMatch: function (loader) {
                        try {
                            if(loader.findClass("org.chromium.base.CommandLine")){
                                console.log("[+]Successfully found loader")
                                console.log(loader);
                                Java.classFactory.loader = loader;
                                let CommandLine = Java.use("org.chromium.base.CommandLine");
                                CommandLine.nativeInit.implementation = function(...args){
                                            this.nativeInit(...args);
                                            this.nativeAppendSwitchWithValue("--js-flags", "--allow-natives-syntax");
                                }
                            }
                        }
                        catch(error){
                            console.log("[!]Find error:" + error)
                        }
                    },
                    onComplete: function () {
                        console.log("[+]onComplete");
                    }
                });
            });
        }
    });
}