Revert "refactor: only create webContents after 'will-attach-webview' (#30311)" (#31785)

This reverts commit 6e43b0bcbf.

shell/browser/api/electron_api_web_view_manager.cc

@@ -28,6 +28,10 @@ void AddGuest(int guest_instance_id,
     electron::WebContentsZoomController::FromWebContents(guest_web_contents)
         ->SetDefaultZoomFactor(zoom_factor);
   }
+
+  WebContentsPreferences::From(guest_web_contents)->Merge(options);
+  // Trigger re-calculation of webkit prefs.
+  guest_web_contents->NotifyPreferencesChanged();
 }
 
 void RemoveGuest(content::WebContents* embedder, int guest_instance_id) {

shell/browser/web_contents_preferences.cc

@@ -176,7 +176,11 @@ void WebContentsPreferences::Clear() {
 void WebContentsPreferences::SetFromDictionary(
     const gin_helper::Dictionary& web_preferences) {
   Clear();
+  Merge(web_preferences);
+}
 
+void WebContentsPreferences::Merge(
+    const gin_helper::Dictionary& web_preferences) {
   web_preferences.Get(options::kPlugins, &plugins_);
   web_preferences.Get(options::kExperimentalFeatures, &experimental_features_);
   web_preferences.Get(options::kNodeIntegration, &node_integration_);

shell/browser/web_contents_preferences.h

@@ -40,6 +40,8 @@ class WebContentsPreferences
   WebContentsPreferences(const WebContentsPreferences&) = delete;
   WebContentsPreferences& operator=(const WebContentsPreferences&) = delete;
 
+  void Merge(const gin_helper::Dictionary& new_web_preferences);
+
   void SetFromDictionary(const gin_helper::Dictionary& new_web_preferences);
 
   // Append command paramters according to preferences.