Remove setupDevtools file

Summary: There is a `setUpDeveloperTools.js` and a `setupDevtools.js` files. While they do set up different devtools it is very confusing to have these two files. This diff inlines one in the other which should bring more clarity.

Reviewed By: gaearon

Differential Revision: D16121236

fbshipit-source-id: 45641c7af9639ede6dc237ac53b763cd804a05c2

Libraries/Core/setUpDeveloperTools.js

@@ -22,7 +22,31 @@ if (__DEV__) {
       // not when debugging in chrome
       // TODO(t12832058) This check is broken
       if (!window.document) {
-        require('./Devtools/setupDevtools');
+        const AppState = require('../AppState/AppState');
+        // $FlowFixMe Module is untyped
+        const reactDevTools = require('react-devtools-core');
+        const getDevServer = require('./Devtools/getDevServer');
+
+        // Don't steal the DevTools from currently active app.
+        // Note: if you add any AppState subscriptions to this file,
+        // you will also need to guard against `AppState.isAvailable`,
+        // or the code will throw for bundles that don't have it.
+        const isAppActive = () => AppState.currentState !== 'background';
+
+        // Get hostname from development server (packager)
+        const devServer = getDevServer();
+        const host = devServer.bundleLoadedFromServer
+          ? devServer.url.replace(/https?:\/\//, '').split(':')[0]
+          : 'localhost';
+
+        reactDevTools.connectToDevTools({
+          isAppActive,
+          host,
+          // Read the optional global variable for backward compatibility.
+          // It was added in https://github.com/facebook/react-native/commit/bf2b435322e89d0aeee8792b1c6e04656c2719a0.
+          port: window.__REACT_DEVTOOLS_PORT__,
+          resolveRNStyle: require('../StyleSheet/flattenStyle'),
+        });
       }
 
       // Set up inspector

jest/setup.js

@@ -27,8 +27,6 @@ global.cancelAnimationFrame = function(id) {
   clearTimeout(id);
 };
 
-jest.mock('../Libraries/Core/Devtools/setupDevtools');
-
 // there's a __mock__ for it.
 jest.setMock(
   '../Libraries/vendor/core/ErrorUtils',