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])`

shell/browser/api/electron_api_web_contents.cc

@@ -1173,6 +1173,11 @@ void WebContents::DidStartLoading() {
 
 void WebContents::DidStopLoading() {
   Emit("did-stop-loading");
+
+  auto* web_preferences = WebContentsPreferences::From(web_contents());
+  if (web_preferences &&
+      web_preferences->IsEnabled(options::kEnablePreferredSizeMode))
+    web_contents()->GetRenderViewHost()->EnablePreferredSizeMode();
 }
 
 bool WebContents::EmitNavigationEvent(
@@ -2903,6 +2908,11 @@ v8::Local<v8::Promise> WebContents::TakeHeapSnapshot(
   return handle;
 }
 
+void WebContents::UpdatePreferredSize(content::WebContents* web_contents,
+                                      const gfx::Size& pref_size) {
+  Emit("preferred-size-changed", pref_size);
+}
+
 // static
 v8::Local<v8::ObjectTemplate> WebContents::FillObjectTemplate(
     v8::Isolate* isolate,

shell/browser/api/electron_api_web_contents.h

@@ -551,6 +551,8 @@ class WebContents : public gin::Wrappable<WebContents>,
   content::JavaScriptDialogManager* GetJavaScriptDialogManager(
       content::WebContents* source) override;
   void OnAudioStateChanged(bool audible) override;
+  void UpdatePreferredSize(content::WebContents* web_contents,
+                           const gfx::Size& pref_size) override;
 
   // content::WebContentsObserver:
   void BeforeUnloadFired(bool proceed,

shell/browser/web_contents_preferences.cc

@@ -143,6 +143,7 @@ WebContentsPreferences::WebContentsPreferences(
   SetDefaultBoolIfUndefined(options::kTextAreasAreResizable, true);
   SetDefaultBoolIfUndefined(options::kWebGL, true);
   SetDefaultBoolIfUndefined(options::kEnableWebSQL, true);
+  SetDefaultBoolIfUndefined(options::kEnablePreferredSizeMode, false);
   bool webSecurity = true;
   SetDefaultBoolIfUndefined(options::kWebSecurity, webSecurity);
   // If webSecurity was explicitly set to false, let's inherit that into

shell/common/options_switches.cc

@@ -191,6 +191,8 @@ const char kEnableRemoteModule[] = "enableRemoteModule";
 
 const char kEnableWebSQL[] = "enableWebSQL";
 
+const char kEnablePreferredSizeMode[] = "enablePreferredSizeMode";
+
 }  // namespace options
 
 namespace switches {

shell/common/options_switches.h

@@ -87,6 +87,7 @@ extern const char kTextAreasAreResizable[];
 extern const char kWebGL[];
 extern const char kNavigateOnDragDrop[];
 extern const char kEnableWebSQL[];
+extern const char kEnablePreferredSizeMode[];
 
 #if BUILDFLAG(ENABLE_BUILTIN_SPELLCHECKER)
 extern const char kSpellcheck[];