Created new PanelStrip base class and make DockedPanelStrip and OverflowPanelStrip its subclasses.

chrome/browser/ui/panels/panel_manager.h

Index: chrome/browser/ui/panels/panel_manager.h
diff --git a/chrome/browser/ui/panels/panel_manager.h b/chrome/browser/ui/panels/panel_manager.h
index f5c9ccf1fabfef2b4243c8f57a577e32e1f9ec0e..120a4d346e828f7706b7a8c7abd3b794aaae6760 100644
--- a/chrome/browser/ui/panels/panel_manager.h
+++ b/chrome/browser/ui/panels/panel_manager.h
@@ -37,7 +37,9 @@ class PanelManager : public AutoHidingDesktopBar::Observer {
   Panel* CreatePanel(Browser* browser);
 
   void Remove(Panel* panel);
-  void RemoveAll();
+
+  // Close all panels (asynchronous). Panels will be removed after closing.
+  void CloseAll();
 
   // Asynchronous confirmation of panel having been removed.
   void OnPanelRemoved(Panel* panel);