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

@@ -53,6 +53,7 @@
     "absolute-path": "^0.0.0",
     "babel": "^5.8.23",
     "babel-core": "^5.8.23",
+    "browser-launcher2": "0.4.6",
     "bser": "^1.0.2",
     "chalk": "^1.1.1",
     "connect": "^2.8.3",

packager/getDevToolsMiddleware.js

@@ -11,8 +11,49 @@
 var execFile = require('child_process').execFile;
 var fs = require('fs');
 var path = require('path');
+var launcher = require('browser-launcher2');
 
-module.exports = function(options) {
+function closeChromeInstance(instance) {
+  return new Promise(function(resolve, reject) {
+    if (!instance) {
+      resolve();
+      return;
+    }
+    instance.stop(function(err) {
+      if (err) {
+        reject(err);
+        return;
+      }
+      resolve();
+    });
+  });
+}
+
+function launchChrome(url, options) {
+  return new Promise(function(resolve, reject) {
+    launcher(function(err, launch) {
+      if (err) {
+        console.error('Failed to initialize browser-launcher2', err);
+        reject(err);
+        return;
+      }
+      launch(url, {
+        browser: 'chrome',
+        options: options,
+      }, function(err, instance) {
+        if (err) {
+          console.error('Failed to launch chrome', err);
+          reject(err);
+          return;
+        }
+        resolve(instance);
+      });
+    });
+  });
+}
+
+module.exports = function(options, isDebuggerConnected) {
+  var chromeInstance;
   return function(req, res, next) {
     if (req.url === '/debugger-ui') {
       var debuggerPath = path.join(__dirname, 'debugger.html');
@@ -29,20 +70,32 @@ module.exports = function(options) {
         'If you still need this, please let us know.'
       );
     } else if (req.url === '/launch-chrome-devtools') {
+      if (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) {
-          if (err) {
-            console.log('Failed to run ' + script, err);
-          }
-          console.log(stdout);
-          console.warn(stderr);
-        }
-      );
-      res.end('OK');
+      closeChromeInstance(chromeInstance)
+        .then(function() {
+          return launchChrome(debuggerURL, chromeOptions)
+        })
+        .then(function(instance) {
+          // Keep a reference to the Chrome instance and unset it if Chrome stops
+          chromeInstance = instance;
+          chromeInstance.on('stop', function() {
+            chromeInstance = null;
+          });
+          res.end('OK');
+        })
+        .catch(function(err) {
+          next(err);
+        });
     } else {
       next();
     }

packager/packager.js

@@ -64,6 +64,9 @@ var options = parseCommandLine([{
   command: 'reset-cache',
   description: 'Removes cached files',
   default: false,
+}, {
+  command: 'dangerouslyDisableChromeDebuggerWebSecurity',
+  description: 'Disable the Chrome debugger\'s same-origin policy'
 }]);
 
 if (options.projectRoots) {
@@ -160,7 +163,13 @@ var server = runServer(options, function() {
   console.log('\nReact packager ready.\n');
 });
 
-webSocketProxy.attachToServer(server, '/debugger-proxy');
+var proxy = webSocketProxy.attachToServer(server, '/debugger-proxy');
+
+function isDebuggerConnected() {
+  // Debugger is connected if the app and at least one browser are connected
+  // to the websocket proxy.
+  return proxy.clientsCount() >= 2;
+}
 
 function getAppMiddleware(options) {
   var transformerPath = options.transformer;
@@ -191,7 +200,7 @@ function runServer(
 ) {
   var app = connect()
     .use(loadRawBodyMiddleware)
-    .use(getDevToolsMiddleware(options))
+    .use(getDevToolsMiddleware(options, isDebuggerConnected))
     .use(openStackFrameInEditorMiddleware)
     .use(statusPageMiddleware)
     .use(systraceProfileMiddleware)

packager/webSocketProxy.js

@@ -57,7 +57,12 @@ function attachToServer(server, path) {
     });
   });
 
-  return wss;
+  return {
+    server: wss,
+    clientsCount: function() {
+      return clients.length;
+    }
+  };
 }
 
 module.exports = {