Revert the patch that has disabled Panels for M53 (https://codereview.chromium.org/2083113002)

chrome/browser/ui/panels/panel_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/panels/panel_manager.h"
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 113 matching lines @@
       wm_type != ui::WM_ICE_WM &&
       wm_type != ui::WM_KWIN &&
       wm_type != ui::WM_METACITY &&
       wm_type != ui::WM_MUFFIN &&
       wm_type != ui::WM_MUTTER &&
       wm_type != ui::WM_XFWM4) {
     return false;
   }
 #endif  // USE_X11 && !OS_CHROMEOS
 
-// Panels are an Eraser target. See http://crbug.com/571511 for details.
-// TODO(dimich): remove the rest of Panels code (except ChromeOS) once
-// erasure is stable.
-#if defined(OS_CHROMEOS)
-  // Without --enable-panels, only support Hangouts on ChromeOS.
+  // Without --enable-panels, only support Hangouts.
   for (const char* id : extension_misc::kHangoutsExtensionIds) {
     if (extension_id == id)
       return true;
   }
-#endif  // OS_CHROMEOS
 
   return false;
 }
 
 // static
 bool PanelManager::IsPanelStackingEnabled() {
   // Stacked panel mode is not supported in linux-aura.
 #if defined(OS_LINUX)
   return false;
 #else
@@ skipping 420 matching lines @@
 void PanelManager::SetMouseWatcher(PanelMouseWatcher* watcher) {
   panel_mouse_watcher_.reset(watcher);
 }
 
 void PanelManager::OnPanelAnimationEnded(Panel* panel) {
   content::NotificationService::current()->Notify(
       chrome::NOTIFICATION_PANEL_BOUNDS_ANIMATIONS_FINISHED,
       content::Source<Panel>(panel),
       content::NotificationService::NoDetails());
 }