Replace applescript with browser-launcher2

This allows...

1. launching Chrome on platforms other than OS X
2. users to launch their own instance of Chrome (e.g. via command line)
   rather than being forced to use the default instance (i.e.
   `tell application "Chrome"` always used the default instance)

`isDebuggerConnected()` addresses the problem in facebook#510 where the dev tools
would only open once per server session.

Add a '--dangerouslyDisableChromeDebuggerWebSecurity' flag to
packager.js to enable Chrome '--disable-web-security' flag.

This allows users to inspect network requests in Chrome by commenting
the xhr polyfill in InitializeJavaScriptAppEngine.js:
  facebook#934 (comment)

Usage:

    node packager.js --dangerouslyDisableChromeDebuggerWebSecurity

or:

    packager.sh --dangerouslyDisableChromeDebuggerWebSecurity

package.json

@@ -49,6 +49,7 @@
     "absolute-path": "0.0.0",
     "babel": "5.8.21",
     "babel-core": "5.8.21",
+    "browser-launcher2": "0.4.6",
     "chalk": "1.0.0",
     "connect": "2.8.3",
     "debug": "2.1.0",

packager/packager.js

@@ -13,6 +13,7 @@ var path = require('path');
 var execFile = require('child_process').execFile;
 var http = require('http');
 var isAbsolutePath = require('absolute-path');
+var launcher = require('browser-launcher2');
 
 var getFlowTypeCheckMiddleware = require('./getFlowTypeCheckMiddleware');
 
@@ -64,6 +65,9 @@ var options = parseCommandLine([{
   type: 'string',
   default: require.resolve('./transformer.js'),
   description: 'Specify a custom transformer to be used (absolute path)'
+}, {
+  command: 'dangerouslyDisableChromeDebuggerWebSecurity',
+  description: 'Disable the Chrome debugger\'s same-origin policy'
 }]);
 
 if (options.projectRoots) {
@@ -192,17 +196,35 @@ function getDevToolsLauncher(options) {
       res.writeHead(200, {'Content-Type': 'text/html'});
       fs.createReadStream(debuggerPath).pipe(res);
     } else if (req.url === '/launch-chrome-devtools') {
+      if (webSocketProxy.isDebuggerConnected()) {
+        // Dev tools are already open; no need to open another session
+        res.end('OK');
+        return;
+      }
       var debuggerURL = 'http://localhost:' + options.port + '/debugger-ui';
-      var script = 'launchChromeDevTools.applescript';
+      var chromeOptions =
+        options.dangerouslyDisableChromeDebuggerWebSecurity ?
+          ['--disable-web-security'] :
+          [];
       console.log('Launching Dev Tools...');
-      execFile(path.join(__dirname, script), [debuggerURL], function(err, stdout, stderr) {
+      launcher(function(err, launch) {
         if (err) {
-          console.log('Failed to run ' + script, err);
+          console.error('Failed to initialize browser-launcher2', err);
+          next(err);
+          return;
         }
-        console.log(stdout);
-        console.warn(stderr);
+        launch(debuggerURL, {
+          browser: 'chrome',
+          options: chromeOptions,
+        }, function(err, instance) {
+          if (err) {
+            console.error('Failed to launch chrome', err);
+            next(err);
+            return;
+          }
+          res.end('OK');
+        });
       });
-      res.end('OK');
     } else {
       next();
     }

packager/webSocketProxy.js

@@ -10,12 +10,13 @@
 
 var WebSocketServer = require('ws').Server;
 
+var clients = [];
+
 function attachToServer(server, path) {
   var wss = new WebSocketServer({
     server: server,
     path: path
   });
-  var clients = [];
 
   function sendSpecial(message) {
     clients.forEach(function (cn) {
@@ -59,6 +60,12 @@ function attachToServer(server, path) {
   });
 }
 
+function isDebuggerConnected() {
+  // Debugger is connected if the app and at least one browser are connected
+  return clients.length >= 2;
+}
+
 module.exports = {
-  attachToServer: attachToServer
-};
+  attachToServer: attachToServer,
+  isDebuggerConnected: isDebuggerConnected,
+};