fix tabs destroyed if switched away during first webview attach

Fix #13798 since "display: none" and then "display: ''" of a webview will cause the guest to (asynchronously) detach and attach again, and by that time we had attached another guest, which causes the original tab to be destroyed since we are attaching a guest to a webview which already has a guest.
Luckily, it doesn't look like this workaround is needed in order to paint the first attachGuest of a webview anymore.

app/renderer/pooledWebviewDisplay.js

@@ -8,16 +8,6 @@ const debounce = require('../../js/lib/debounce')
 
 let i = 0
 
-function ensurePaintWebviewFirstAttach (webview, cb = () => {}) {
-  window.requestAnimationFrame(() => {
-    webview.style.display = 'none'
-    window.requestAnimationFrame(() => {
-      webview.style.display = ''
-      window.requestAnimationFrame(cb)
-    })
-  })
-}
-
 function ensurePaintWebviewSubsequentAttach (webview, cb = () => {}) {
   webview.style.top = '1px'
   window.requestAnimationFrame(() => {
@@ -165,7 +155,6 @@ module.exports = class WebviewDisplay {
 
     this.attachingToTabId = tabId
     const t0 = window.performance.now()
-    let timeoutHandleBumpView = null
     const fnEnd = () => {
       if (this.shouldLogEvents) {
         console.groupEnd()
@@ -179,7 +168,7 @@ module.exports = class WebviewDisplay {
       // size has changed or forced to.
       if (!toAttachWebview.isSubsequentAttach) {
         toAttachWebview.isSubsequentAttach = true
-        ensurePaintWebviewFirstAttach(toAttachWebview, showAttachedView)
+        showAttachedView()
       } else {
         ensurePaintWebviewSubsequentAttach(toAttachWebview, showAttachedView)
       }
@@ -290,7 +279,6 @@ module.exports = class WebviewDisplay {
         case 'will-destroy':
         case 'destroyed':
           // don't need to bump view
-          clearTimeout(timeoutHandleBumpView)
           remote.unregisterEvents(tabId, tabEventHandler)
           onDestroyedInsteadOfAttached()
           break
@@ -302,7 +290,6 @@ module.exports = class WebviewDisplay {
           // we're done displaying
           if (!handled) {
             // don't need to bump view
-            clearTimeout(timeoutHandleBumpView)
             onToAttachDidAttach()
             handled = true
           }
@@ -331,8 +318,6 @@ module.exports = class WebviewDisplay {
       // setImmediate is a bit of a hacky way to ensure that registerEvents handler is registered
       setImmediate(() => toAttachWebview.attachGuest(guestInstanceId, webContents))
       this.debugLog(`swapWebviewOnAttach: Waiting.... ${window.performance.now() - t0}ms`)
-      // another workaround for not getting did-attach on webview, set a timeout and then hide / show view
-      timeoutHandleBumpView = window.setTimeout(ensurePaintWebviewFirstAttach.bind(null, toAttachWebview), 2000)
     })
   }