Don't delete Primary root window and monitor

ash/monitor/monitor_controller.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 "ash/monitor/monitor_controller.h"
 
 #include "ash/monitor/multi_monitor_manager.h"
 #include "ash/monitor/secondary_monitor_view.h"
 #include "ash/shell.h"
 #include "ash/wm/base_layout_manager.h"
@@ skipping 40 matching lines @@
   root_windows_.erase(monitor);
   STLDeleteContainerPairSecondPointers(
       root_windows_.begin(), root_windows_.end());
 }
 
 void MonitorController::OnMonitorBoundsChanged(const aura::Monitor* monitor) {
   root_windows_[monitor]->SetHostBounds(monitor->bounds());
 }
 
 void MonitorController::OnMonitorAdded(aura::Monitor* monitor) {
+  if (root_windows_.empty()) {
+    root_windows_[monitor] = Shell::GetRootWindow();
+    Shell::GetRootWindow()->SetHostBounds(monitor->bounds());
+    return;
+  }
   aura::RootWindow* root = aura::Env::GetInstance()->monitor_manager()->
       CreateRootWindowForMonitor(monitor);
   root_windows_[monitor] = root;
   SetupAsSecondaryMonitor(root);
 }
 
 void MonitorController::OnMonitorRemoved(const aura::Monitor* monitor) {
   aura::RootWindow* root = root_windows_[monitor];
-  root_windows_.erase(monitor);
-  delete root;
+  DCHECK(root);
+  // Primary monitor should never be removed by MonitorManager.
+  DCHECK(root != Shell::GetRootWindow());
+  // Monitor for root window will be deleted when the Primary RootWindow
+  // is deleted by the Shell.
+  if (root != Shell::GetRootWindow()) {
+    root_windows_.erase(monitor);
+    delete root;
+  }
 }
 
 void MonitorController::Init() {
   aura::MonitorManager* monitor_manager =
       aura::Env::GetInstance()->monitor_manager();
   for (size_t i = 0; i < monitor_manager->GetNumMonitors(); ++i) {
     aura::Monitor* monitor = monitor_manager->GetMonitorAt(i);
     const aura::Monitor* key = monitor;
     if (i == 0) {
       // Primary monitor
       root_windows_[key] = Shell::GetRootWindow();
       Shell::GetRootWindow()->SetHostBounds(monitor->bounds());
     } else {
       aura::RootWindow* root =
           monitor_manager->CreateRootWindowForMonitor(monitor);
       root_windows_[key] = root;
       SetupAsSecondaryMonitor(root);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace ash