feat(Launcher): allow the default arguments to be overridden (#1623)

This patch:
- adds `puppeteer.defaultArgs()` method to get default arguments that are used to launch chrome
- adds `ignoreDefaultArgs` option to `puppeteer.launch` to avoid using default puppeteer arguments

Fixes #872

docs/api.md

@@ -10,6 +10,7 @@
 - [Environment Variables](#environment-variables)
 - [class: Puppeteer](#class-puppeteer)
   * [puppeteer.connect(options)](#puppeteerconnectoptions)
+  * [puppeteer.defaultArgs()](#puppeteerdefaultargs)
   * [puppeteer.executablePath()](#puppeteerexecutablepath)
   * [puppeteer.launch([options])](#puppeteerlaunchoptions)
 - [class: Browser](#class-browser)
@@ -246,6 +247,9 @@ puppeteer.launch().then(async browser => {
 
 This methods attaches Puppeteer to an existing Chromium instance.
 
+#### puppeteer.defaultArgs()
+- returns: <[Array]<[string]>> The default flags that Chromium will be launched with.
+
 #### puppeteer.executablePath()
 - returns: <[string]> A path where Puppeteer expects to find bundled Chromium. Chromium might not exist there if the download was skipped with [`PUPPETEER_SKIP_CHROMIUM_DOWNLOAD`](#environment-variables).
 
@@ -256,6 +260,7 @@ This methods attaches Puppeteer to an existing Chromium instance.
   - `executablePath` <[string]> Path to a Chromium or Chrome executable to run instead of bundled Chromium. If `executablePath` is a relative path, then it is resolved relative to [current working directory](https://nodejs.org/api/process.html#process_process_cwd).
   - `slowMo` <[number]> Slows down Puppeteer operations by the specified amount of milliseconds. Useful so that you can see what is going on.
   - `args` <[Array]<[string]>> Additional arguments to pass to the browser instance. List of Chromium flags can be found [here](http://peter.sh/experiments/chromium-command-line-switches/).
+  - `ignoreDefaultArgs` <[boolean]> Do not use [`puppeteer.defaultArgs()`](#puppeteerdefaultargs). Dangerous option; use with care. Defaults to `false`.
   - `handleSIGINT` <[boolean]> Close browser process on Ctrl-C. Defaults to `true`.
   - `handleSIGTERM` <[boolean]> Close browser process on SIGTERM. Defaults to `true`.
   - `handleSIGHUP` <[boolean]> Close browser process on SIGHUP. Defaults to `true`.
@@ -269,12 +274,12 @@ This methods attaches Puppeteer to an existing Chromium instance.
 The method launches a browser instance with given arguments. The browser will be closed when the parent node.js process is closed.
 
 > **NOTE** Puppeteer can also be used to control the Chrome browser, but it works best with the version of Chromium it is bundled with. There is no
- guarantee it will work with any other version. Use `executablePath` option with extreme caution.  
+ guarantee it will work with any other version. Use `executablePath` option with extreme caution.
 If Google Chrome (rather than Chromium) is preferred, a [Chrome Canary](https://www.google.com/chrome/browser/canary.html) or [Dev Channel](https://www.chromium.org/getting-involved/dev-channel) build is suggested.
 >
 > In [puppeteer.launch([options])](#puppeteerlaunchoptions) above, any mention of Chromium also applies to Chrome.
 >
-> See [`this article`](https://www.howtogeek.com/202825/what%E2%80%99s-the-difference-between-chromium-and-chrome/) for a description 
+> See [`this article`](https://www.howtogeek.com/202825/what%E2%80%99s-the-difference-between-chromium-and-chrome/) for a description
   of the differences between Chromium and Chrome. [`This article`](https://chromium.googlesource.com/chromium/src/+/lkcr/docs/chromium_browser_vs_google_chrome.md) describes some differences for Linux users.
 
 ### class: Browser

lib/Launcher.js

@@ -61,10 +61,13 @@ class Launcher {
   static async launch(options) {
     options = Object.assign({}, options || {});
     let temporaryUserDataDir = null;
-    const chromeArguments = [].concat(DEFAULT_ARGS);
+    const chromeArguments = [];
+    if (!options.ignoreDefaultArgs)
+      chromeArguments.push(...DEFAULT_ARGS);
+
     if (options.appMode)
       options.headless = false;
-    else
+    else if (!options.ignoreDefaultArgs)
       chromeArguments.push(...AUTOMATION_ARGS);
 
     if (!options.args || !options.args.some(arg => arg.startsWith('--user-data-dir'))) {
@@ -172,6 +175,13 @@ class Launcher {
     }
   }
 
+  /**
+   * @return {!Array<string>}
+   */
+  static defaultArgs() {
+    return DEFAULT_ARGS.concat(AUTOMATION_ARGS);
+  }
+
   /**
    * @return {string}
    */

lib/Puppeteer.js

@@ -39,6 +39,13 @@ class Puppeteer {
   static executablePath() {
     return Launcher.executablePath();
   }
+
+  /**
+   * @return {!Array<string>}
+   */
+  static defaultArgs() {
+    return Launcher.defaultArgs();
+  }
 }
 
 module.exports = Puppeteer;

test/test.js

@@ -202,6 +202,10 @@ describe('Puppeteer', function() {
       rm(userDataDir);
       expect(cookie).toBe('foo=true');
     });
+    it('should return the default chrome arguments', async() => {
+      const args = puppeteer.defaultArgs();
+      expect(args).toContain('--no-first-run');
+    });
   });
   describe('Puppeteer.connect', function() {
     it('should be able to connect multiple times to the same browser', async({server}) => {