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": "^5.8.23",
     "babel-core": "^5.8.23",
+    "browser-launcher2": "0.4.6",
     "bser": "^1.0.2",
     "chalk": "^1.1.1",
     "connect": "^2.8.3",

packager/packager.js

@@ -13,6 +13,7 @@ var path = require('path');
 var childProcess = require('child_process');
 var http = require('http');
 var isAbsolutePath = require('absolute-path');
+var launcher = require('browser-launcher2');
 
 var getFlowTypeCheckMiddleware = require('./getFlowTypeCheckMiddleware');
 
@@ -57,6 +58,9 @@ 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) {
@@ -153,7 +157,7 @@ var server = runServer(options, function() {
   console.log('\nReact packager ready.\n');
 });
 
-webSocketProxy.attachToServer(server, '/debugger-proxy');
+var proxy = webSocketProxy.attachToServer(server, '/debugger-proxy');
 
 function loadRawBody(req, res, next) {
   req.rawBody = '';
@@ -178,7 +182,47 @@ function openStackFrameInEditor(req, res, next) {
   }
 }
 
+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);
+      });
+    });
+  });
+}
+
 function getDevToolsLauncher(options) {
+  var chromeInstance;
   return function(req, res, next) {
     if (req.url === '/debugger-ui') {
       var debuggerPath = path.join(__dirname, 'debugger.html');
@@ -191,17 +235,32 @@ function getDevToolsLauncher(options) {
       fs.createReadStream(workerPath).pipe(res);
 
     } else if (req.url === '/launch-chrome-devtools') {
+      if (proxy.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...');
-      childProcess.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/webSocketProxy.js

@@ -57,6 +57,13 @@ function attachToServer(server, path) {
       });
     });
   });
+
+  return {
+    isDebuggerConnected: function() {
+      // Debugger is connected if the app and at least one browser are connected
+      return clients.length >= 2;
+    }
+  };
 }
 
 module.exports = {