feat: add contents.getBackgroundThrottling() + backgroundThrottling property (#21036)

docs/api/modernization/property-updates.md

@@ -34,6 +34,7 @@ The Electron team is currently undergoing an initiative to convert separate gett
   * `fullscreenable`
   * `movable`
   * `closable`
+  * `backgroundThrottling`
 * `NativeImage`
   * `isMacTemplateImage`
 * `SystemPreferences` module

docs/api/web-contents.md

@@ -1812,6 +1812,11 @@ Returns `Promise<void>` - Indicates whether the snapshot has been created succes
 
 Takes a V8 heap snapshot and saves it to `filePath`.
 
+#### `contents.getBackgroundThrottling()`
+
+Returns `Boolean` - whether or not this WebContents will throttle animations and timers
+when the page becomes backgrounded. This also affects the Page Visibility API.
+
 #### `contents.setBackgroundThrottling(allowed)`
 
 * `allowed` Boolean
@@ -1879,3 +1884,8 @@ A [`Debugger`](debugger.md) instance for this webContents.
 [event-emitter]: https://nodejs.org/api/events.html#events_class_eventemitter
 [SCA]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
 [`postMessage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage
+
+#### `contents.backgroundThrottling`
+
+A `Boolean` property that determines whether or not this WebContents will throttle animations and timers
+when the page becomes backgrounded. This also affects the Page Visibility API.