Let Chromium manage document.visibilityState and document.hidden

Chromium already includes the necessary plumbing to manage the
visibility properties and `visibilitychange` event so this gets rid of
most of our custom logic for `BrowserWindow` and `BrowserView`.

Note that `webview` remains unchanged and is still affected by the issues
listed below.

User facing changes:

- The `document` visibility properties and `visibilitychange` event are
  now also updated/fired in response to occlusion changes on macOS. In
  other words, `document.visibilityState` will now be `hidden` on macOS
  if the window is occluded by another window.

- Previously, `visibilitychange` was also fired by *both* Electron and
  Chromium in some cases (e.g. when hiding the window). Now it is only
  fired by Chromium so you no longer get duplicate events.

- The visiblity state of `BrowserWindow`s created with `{ show: false }`
  is now initially `visible` until the window is shown and hidden.

- The visibility state of `BrowserWindow`s with `backgroundThrottling`
  disabled is now permanently `visible`.

This should also fix #6860 (but not for `webview`).

lib/renderer/window-setup.js

@@ -175,27 +175,35 @@ module.exports = (ipcRenderer, guestInstanceId, openerId, hiddenPage, usesNative
     }
   })
 
-  // The initial visibilityState.
-  let cachedVisibilityState = hiddenPage ? 'hidden' : 'visible'
+  if (guestInstanceId != null) {
+    // Webview `document.visibilityState` tracks window visibility (and ignores
+    // the actual <webview> element visibility) for backwards compatibility.
+    // See discussion in #9178.
+    //
+    // Note that this results in duplicate visibilitychange events (since
+    // Chromium also fires them) and potentially incorrect visibility change.
+    // We should reconsider this decision for Electron 2.0.
+    let cachedVisibilityState = hiddenPage ? 'hidden' : 'visible'
 
-  // Subscribe to visibilityState changes.
-  ipcRenderer.on('ELECTRON_RENDERER_WINDOW_VISIBILITY_CHANGE', function (event, visibilityState) {
-    if (cachedVisibilityState !== visibilityState) {
-      cachedVisibilityState = visibilityState
-      document.dispatchEvent(new Event('visibilitychange'))
-    }
-  })
+    // Subscribe to visibilityState changes.
+    ipcRenderer.on('ELECTRON_GUEST_INSTANCE_VISIBILITY_CHANGE', function (event, visibilityState) {
+      if (cachedVisibilityState !== visibilityState) {
+        cachedVisibilityState = visibilityState
+        document.dispatchEvent(new Event('visibilitychange'))
+      }
+    })
 
-  // Make document.hidden and document.visibilityState return the correct value.
-  defineProperty(document, 'hidden', {
-    get: function () {
-      return cachedVisibilityState !== 'visible'
-    }
-  })
+    // Make document.hidden and document.visibilityState return the correct value.
+    defineProperty(document, 'hidden', {
+      get: function () {
+        return cachedVisibilityState !== 'visible'
+      }
+    })
 
-  defineProperty(document, 'visibilityState', {
-    get: function () {
-      return cachedVisibilityState
-    }
-  })
+    defineProperty(document, 'visibilityState', {
+      get: function () {
+        return cachedVisibilityState
+      }
+    })
+  }
 }