Add trusted-set-attr scriptlet

@trustedScriptlet trusted-set-attr

@description
Sets the specified attribute on the specified elements. This scriptlet runs
once when the page loads then afterward on DOM mutations.

Reference: https://github.com/AdguardTeam/Scriptlets/blob/master/wiki/about-trusted-scriptlets.md#-%EF%B8%8F-trusted-set-attr

@param selector
A CSS selector for the elements to target.

@param attr
The name of the attribute to modify.

@param value
The new value of the attribute. Since the scriptlet requires a trusted
source, the value can be anything.

=====

Additionally, start to move scriptlets into their own source files
for easier maintenance and code review.

assets/resources/run-at.js

@@ -0,0 +1,64 @@
+/*******************************************************************************
+
+    uBlock Origin - a comprehensive, efficient content blocker
+    Copyright (C) 2019-present Raymond Hill
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see {http://www.gnu.org/licenses/}.
+
+    Home: https://github.com/gorhill/uBlock
+
+    The scriptlets below are meant to be injected only into a
+    web page context.
+*/
+
+import { safeSelf } from './safe-self.js';
+
+/* eslint no-prototype-builtins: 0 */
+
+/******************************************************************************/
+
+export function runAt(fn, when) {
+    const intFromReadyState = state => {
+        const targets = {
+            'loading': 1, 'asap': 1,
+            'interactive': 2, 'end': 2, '2': 2,
+            'complete': 3, 'idle': 3, '3': 3,
+        };
+        const tokens = Array.isArray(state) ? state : [ state ];
+        for ( const token of tokens ) {
+            const prop = `${token}`;
+            if ( targets.hasOwnProperty(prop) === false ) { continue; }
+            return targets[prop];
+        }
+        return 0;
+    };
+    const runAt = intFromReadyState(when);
+    if ( intFromReadyState(document.readyState) >= runAt ) {
+        fn(); return;
+    }
+    const onStateChange = ( ) => {
+        if ( intFromReadyState(document.readyState) < runAt ) { return; }
+        fn();
+        safe.removeEventListener.apply(document, args);
+    };
+    const safe = safeSelf();
+    const args = [ 'readystatechange', onStateChange, { capture: true } ];
+    safe.addEventListener.apply(document, args);
+}
+runAt.details = {
+    name: 'run-at.fn',
+    dependencies: [
+        safeSelf,
+    ],
+};

assets/resources/safe-self.js

@@ -0,0 +1,218 @@
+/*******************************************************************************
+
+    uBlock Origin - a comprehensive, efficient content blocker
+    Copyright (C) 2019-present Raymond Hill
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see {http://www.gnu.org/licenses/}.
+
+    Home: https://github.com/gorhill/uBlock
+
+    The scriptlets below are meant to be injected only into a
+    web page context.
+*/
+
+/******************************************************************************/
+
+// Externally added to the private namespace in which scriptlets execute.
+/* global scriptletGlobals */
+
+export function safeSelf() {
+    if ( scriptletGlobals.safeSelf ) {
+        return scriptletGlobals.safeSelf;
+    }
+    const self = globalThis;
+    const safe = {
+        'Array_from': Array.from,
+        'Error': self.Error,
+        'Function_toStringFn': self.Function.prototype.toString,
+        'Function_toString': thisArg => safe.Function_toStringFn.call(thisArg),
+        'Math_floor': Math.floor,
+        'Math_max': Math.max,
+        'Math_min': Math.min,
+        'Math_random': Math.random,
+        'Object': Object,
+        'Object_defineProperty': Object.defineProperty.bind(Object),
+        'Object_defineProperties': Object.defineProperties.bind(Object),
+        'Object_fromEntries': Object.fromEntries.bind(Object),
+        'Object_getOwnPropertyDescriptor': Object.getOwnPropertyDescriptor.bind(Object),
+        'RegExp': self.RegExp,
+        'RegExp_test': self.RegExp.prototype.test,
+        'RegExp_exec': self.RegExp.prototype.exec,
+        'Request_clone': self.Request.prototype.clone,
+        'String_fromCharCode': String.fromCharCode,
+        'XMLHttpRequest': self.XMLHttpRequest,
+        'addEventListener': self.EventTarget.prototype.addEventListener,
+        'removeEventListener': self.EventTarget.prototype.removeEventListener,
+        'fetch': self.fetch,
+        'JSON': self.JSON,
+        'JSON_parseFn': self.JSON.parse,
+        'JSON_stringifyFn': self.JSON.stringify,
+        'JSON_parse': (...args) => safe.JSON_parseFn.call(safe.JSON, ...args),
+        'JSON_stringify': (...args) => safe.JSON_stringifyFn.call(safe.JSON, ...args),
+        'log': console.log.bind(console),
+        // Properties
+        logLevel: 0,
+        // Methods
+        makeLogPrefix(...args) {
+            return this.sendToLogger && `[${args.join(' \u205D ')}]` || '';
+        },
+        uboLog(...args) {
+            if ( this.sendToLogger === undefined ) { return; }
+            if ( args === undefined || args[0] === '' ) { return; }
+            return this.sendToLogger('info', ...args);
+
+        },
+        uboErr(...args) {
+            if ( this.sendToLogger === undefined ) { return; }
+            if ( args === undefined || args[0] === '' ) { return; }
+            return this.sendToLogger('error', ...args);
+        },
+        escapeRegexChars(s) {
+            return s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+        },
+        initPattern(pattern, options = {}) {
+            if ( pattern === '' ) {
+                return { matchAll: true, expect: true };
+            }
+            const expect = (options.canNegate !== true || pattern.startsWith('!') === false);
+            if ( expect === false ) {
+                pattern = pattern.slice(1);
+            }
+            const match = /^\/(.+)\/([gimsu]*)$/.exec(pattern);
+            if ( match !== null ) {
+                return {
+                    re: new this.RegExp(
+                        match[1],
+                        match[2] || options.flags
+                    ),
+                    expect,
+                };
+            }
+            if ( options.flags !== undefined ) {
+                return {
+                    re: new this.RegExp(this.escapeRegexChars(pattern),
+                        options.flags
+                    ),
+                    expect,
+                };
+            }
+            return { pattern, expect };
+        },
+        testPattern(details, haystack) {
+            if ( details.matchAll ) { return true; }
+            if ( details.re ) {
+                return this.RegExp_test.call(details.re, haystack) === details.expect;
+            }
+            return haystack.includes(details.pattern) === details.expect;
+        },
+        patternToRegex(pattern, flags = undefined, verbatim = false) {
+            if ( pattern === '' ) { return /^/; }
+            const match = /^\/(.+)\/([gimsu]*)$/.exec(pattern);
+            if ( match === null ) {
+                const reStr = this.escapeRegexChars(pattern);
+                return new RegExp(verbatim ? `^${reStr}$` : reStr, flags);
+            }
+            try {
+                return new RegExp(match[1], match[2] || undefined);
+            }
+            catch(ex) {
+            }
+            return /^/;
+        },
+        getExtraArgs(args, offset = 0) {
+            const entries = args.slice(offset).reduce((out, v, i, a) => {
+                if ( (i & 1) === 0 ) {
+                    const rawValue = a[i+1];
+                    const value = /^\d+$/.test(rawValue)
+                        ? parseInt(rawValue, 10)
+                        : rawValue;
+                    out.push([ a[i], value ]);
+                }
+                return out;
+            }, []);
+            return this.Object_fromEntries(entries);
+        },
+        onIdle(fn, options) {
+            if ( self.requestIdleCallback ) {
+                return self.requestIdleCallback(fn, options);
+            }
+            return self.requestAnimationFrame(fn);
+        },
+        offIdle(id) {
+            if ( self.requestIdleCallback ) {
+                return self.cancelIdleCallback(id);
+            }
+            return self.cancelAnimationFrame(id);
+        }
+    };
+    scriptletGlobals.safeSelf = safe;
+    if ( scriptletGlobals.bcSecret === undefined ) { return safe; }
+    // This is executed only when the logger is opened
+    safe.logLevel = scriptletGlobals.logLevel || 1;
+    let lastLogType = '';
+    let lastLogText = '';
+    let lastLogTime = 0;
+    safe.toLogText = (type, ...args) => {
+        if ( args.length === 0 ) { return; }
+        const text = `[${document.location.hostname || document.location.href}]${args.join(' ')}`;
+        if ( text === lastLogText && type === lastLogType ) {
+            if ( (Date.now() - lastLogTime) < 5000 ) { return; }
+        }
+        lastLogType = type;
+        lastLogText = text;
+        lastLogTime = Date.now();
+        return text;
+    };
+    try {
+        const bc = new self.BroadcastChannel(scriptletGlobals.bcSecret);
+        let bcBuffer = [];
+        safe.sendToLogger = (type, ...args) => {
+            const text = safe.toLogText(type, ...args);
+            if ( text === undefined ) { return; }
+            if ( bcBuffer === undefined ) {
+                return bc.postMessage({ what: 'messageToLogger', type, text });
+            }
+            bcBuffer.push({ type, text });
+        };
+        bc.onmessage = ev => {
+            const msg = ev.data;
+            switch ( msg ) {
+            case 'iamready!':
+                if ( bcBuffer === undefined ) { break; }
+                bcBuffer.forEach(({ type, text }) =>
+                    bc.postMessage({ what: 'messageToLogger', type, text })
+                );
+                bcBuffer = undefined;
+                break;
+            case 'setScriptletLogLevelToOne':
+                safe.logLevel = 1;
+                break;
+            case 'setScriptletLogLevelToTwo':
+                safe.logLevel = 2;
+                break;
+            }
+        };
+        bc.postMessage('areyouready?');
+    } catch(_) {
+        safe.sendToLogger = (type, ...args) => {
+            const text = safe.toLogText(type, ...args);
+            if ( text === undefined ) { return; }
+            safe.log(`uBO ${text}`);
+        };
+    }
+    return safe;
+}
+safeSelf.details = {
+    name: 'safe-self.fn',
+};