feat: add custom debugging port option

docs/api.md

@@ -462,6 +462,7 @@ This methods attaches Puppeteer to an existing Chromium instance.
   - `args` <[Array]<[string]>> Additional arguments to pass to the browser instance. The list of Chromium flags can be found [here](http://peter.sh/experiments/chromium-command-line-switches/).
   - `userDataDir` <[string]> Path to a [User Data Directory](https://chromium.googlesource.com/chromium/src/+/master/docs/user_data_dir.md).
   - `devtools` <[boolean]> Whether to auto-open a DevTools panel for each tab. If this option is `true`, the `headless` option will be set `false`.
+  - `debuggingPort` <[number]> Specify custom debugging port. Pass `0` to discover a random port. Defaults to `0`.
 - returns: <[Array]<[string]>>
 
 The default flags that Chromium will be launched with.
@@ -537,6 +538,7 @@ try {
   - `timeout` <[number]> Maximum time in milliseconds to wait for the browser instance to start. Defaults to `30000` (30 seconds). Pass `0` to disable timeout.
   - `dumpio` <[boolean]> Whether to pipe the browser process stdout and stderr into `process.stdout` and `process.stderr`. Defaults to `false`.
   - `userDataDir` <[string]> Path to a [User Data Directory](https://chromium.googlesource.com/chromium/src/+/master/docs/user_data_dir.md).
+  - `debuggingPort` <[number]> Specify custom debugging port. Pass `0` to discover a random port. Defaults to `0`.
   - `env` <[Object]> Specify environment variables that will be visible to the browser. Defaults to `process.env`.
   - `devtools` <[boolean]> Whether to auto-open a DevTools panel for each tab. If this option is `true`, the `headless` option will be set `false`.
   - `pipe` <[boolean]> Connects to the browser over a pipe instead of a WebSocket. Defaults to `false`.

lib/Launcher.js

@@ -235,7 +235,8 @@ class Launcher {
       devtools = false,
       headless = !devtools,
       args = [],
-      userDataDir = null
+      userDataDir = null,
+      debuggingPort = null
     } = options;
     const chromeArguments = [...DEFAULT_ARGS];
     if (userDataDir)
@@ -249,6 +250,8 @@ class Launcher {
           '--mute-audio'
       );
     }
+    if (debuggingPort)
+      chromeArguments.push(`--remote-debugging-port=${debuggingPort}`);
     if (args.every(arg => arg.startsWith('-')))
       chromeArguments.push('about:blank');
     chromeArguments.push(...args);
@@ -418,6 +421,7 @@ function getWSEndpoint(browserURL) {
  * @property {Array<string>=} args
  * @property {string=} userDataDir
  * @property {boolean=} devtools
+ * @property {number=} debuggingPort
  */
 
 /**