feat: add webPreferences.enablePreferredSizeMode (#25874)

* feat: add preferredSizeMode preference

* docs: webPreferences.preferredSizeMode and event

* docs: better explain preferred size

* docs: small improvement

* refactor: preferredSizeMode -> enablePreferredSizeMode

docs/api/browser-window.md

@@ -398,6 +398,11 @@ It creates a new `BrowserWindow` with native properties as set by the `options`.
       * `bypassHeatCheck` - Bypass code caching heuristics but with lazy compilation
       * `bypassHeatCheckAndEagerCompile` - Same as above except compilation is eager.
       Default policy is `code`.
+    * `enablePreferredSizeMode` Boolean (optional) - Whether to enable
+      preferred size mode. The preferred size is the minimum size needed to
+      contain the layout of the document—without requiring scrolling. Enabling
+      this will cause the `preferred-size-changed` event to be emitted on the
+      `WebContents` when the preferred size changes. Default is `false`.
 
 When setting minimum or maximum window size with `minWidth`/`maxWidth`/
 `minHeight`/`maxHeight`, it only constrains the users. It won't prevent you from

docs/api/web-contents.md

@@ -837,6 +837,19 @@ Emitted when `remote.getCurrentWebContents()` is called in the renderer process.
 Calling `event.preventDefault()` will prevent the object from being returned.
 Custom value can be returned by setting `event.returnValue`.
 
+#### Event: 'preferred-size-changed'
+
+Returns:
+
+* `event` Event
+* `preferredSize` [Size](structures/size.md) - The minimum size needed to
+  contain the layout of the document—without requiring scrolling.
+
+Emitted when the `WebContents` preferred size has changed.
+
+This event will only be emitted when `enablePreferredSizeMode` is set to `true`
+in `webPreferences`.
+
 ### Instance Methods
 
 #### `contents.loadURL(url[, options])`