Implement sidebar support for extension action popups

extensions/browser/extension_system.cc

Index: extensions/browser/extension_system.cc
diff --git a/extensions/browser/extension_system.cc b/extensions/browser/extension_system.cc
index fc2abc0a8f0eef1be6dfb1f9bab7cd2aba9e650a..dbfbb723380732adfd0cae7616bb31d820a60e1b 100644
--- a/extensions/browser/extension_system.cc
+++ b/extensions/browser/extension_system.cc
@@ -23,4 +23,8 @@ ExtensionSystem* ExtensionSystem::Get(content::BrowserContext* context) {
       ->GetForBrowserContext(context);
 }
 
+SidebarManager* ExtensionSystem::sidebar_manager() {
+  return nullptr;
+}
+
 }  // namespace extensions