refactor: clean up the default app implementation (#14719)

* Disable nodeIntegration
* Enable contextIsolation
* Re-implement the CSP security check to handle running in
contextIsolation
* Disable bad DCHECKS for the promise helper
* Remove the unused "-d" flag for the electron binary
* Added a way to hide the default help output for electron devs who
don't want to see it every time

default_app/default_app.js

@@ -8,28 +8,32 @@ app.on('window-all-closed', () => {
   app.quit()
 })
 
-exports.load = (appUrl) => {
-  app.on('ready', () => {
-    const options = {
-      width: 900,
-      height: 600,
-      autoHideMenuBar: true,
-      backgroundColor: '#FFFFFF',
-      webPreferences: {
-        nodeIntegrationInWorker: true
-      },
-      useContentSize: true,
-      show: false
-    }
-    if (process.platform === 'linux') {
-      options.icon = path.join(__dirname, 'icon.png')
-    }
+exports.load = async (appUrl) => {
+  await app.whenReady()
 
-    mainWindow = new BrowserWindow(options)
+  const options = {
+    width: 900,
+    height: 600,
+    autoHideMenuBar: true,
+    backgroundColor: '#FFFFFF',
+    webPreferences: {
+      contextIsolation: true,
+      nodeIntegration: false,
+      preload: path.resolve(__dirname, 'renderer.js'),
+      webviewTag: false
+    },
+    useContentSize: true,
+    show: false
+  }
 
-    mainWindow.on('ready-to-show', () => mainWindow.show())
+  if (process.platform === 'linux') {
+    options.icon = path.join(__dirname, 'icon.png')
+  }
 
-    mainWindow.loadURL(appUrl)
-    mainWindow.focus()
-  })
+  mainWindow = new BrowserWindow(options)
+
+  mainWindow.on('ready-to-show', () => mainWindow.show())
+
+  mainWindow.loadURL(appUrl)
+  mainWindow.focus()
 }