Replace applescript with https://github.com/sindresorhus/opn

Summary: This allows opening the Chrome debugger on OS X, Linux, and Windows, and succeeds the previous PR which used [browser-launcher2](https://github.com/benderjs/browser-launcher2) and included a `--dangerouslyDisableChromeDebuggerWebSecurity` option: https://github.com/facebook/react-native/pull/2406

[opn](https://github.com/sindresorhus/opn) is cross-platform and much simpler than browser-launcher2 (since we don't have to manage the opened Chrome instance; the OS will just use the default instance).
Closes https://github.com/facebook/react-native/pull/3394

Reviewed By: mkonicek

Differential Revision: D2550996

Pulled By: frantic

fb-gh-sync-id: fa4cbe55542562f30f77e0a6ab4bc53980ee13aa

private-cli/src/server/runServer.js

@@ -20,11 +20,13 @@ const path = require('path');
 const ReactPackager = require('../../../packager/react-packager');
 const statusPageMiddleware = require('../../../packager/statusPageMiddleware.js');
 const systraceProfileMiddleware = require('../../../packager/systraceProfileMiddleware.js');
+const webSocketProxy = require('../../../packager/webSocketProxy.js');
 
 function runServer(args, config, readyCallback) {
+  var wsProxy = null;
   const app = connect()
     .use(loadRawBodyMiddleware)
-    .use(getDevToolsMiddleware(args))
+    .use(getDevToolsMiddleware(args, () => wsProxy && wsProxy.isChromeConnected()))
     .use(openStackFrameInEditorMiddleware)
     .use(statusPageMiddleware)
     .use(systraceProfileMiddleware)
@@ -39,7 +41,15 @@ function runServer(args, config, readyCallback) {
     .use(connect.compress())
     .use(connect.errorHandler());
 
-  return http.createServer(app).listen(args.port, '::', readyCallback);
+  const serverInstance = http.createServer(app).listen(
+    args.port,
+    '::',
+    function() {
+      wsProxy = webSocketProxy.attachToServer(serverInstance, '/debugger-proxy');
+      webSocketProxy.attachToServer(serverInstance, '/devtools');
+      readyCallback();
+    }
+  );
 }
 
 function getAppMiddleware(args, config) {

private-cli/src/server/server.js

@@ -15,7 +15,6 @@ const parseCommandLine = require('../../../packager/parseCommandLine');
 const path = require('path');
 const Promise = require('promise');
 const runServer = require('./runServer');
-const webSocketProxy = require('../../../packager/webSocketProxy.js');
 
 /**
  * Starts the React Native Packager Server.
@@ -138,12 +137,9 @@ function _server(argv, config, resolve, reject) {
 }
 
 function startServer(args, config) {
-  const serverInstance = runServer(args, config, () =>
+  runServer(args, config, () =>
     console.log('\nReact packager ready.\n')
   );
-
-  webSocketProxy.attachToServer(serverInstance, '/debugger-proxy');
-  webSocketProxy.attachToServer(serverInstance, '/devtools');
 }
 
 function argToArray(arg) {