Don't delete Primary root window and monitor

ash/monitor/multi_monitor_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 "ash/monitor/multi_monitor_manager.h"
 
 #include <string>
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 72 matching lines @@
 
   if (monitors_.size() < new_monitors.size()) {
     // New monitors added
     for (size_t i = min; i < new_monitors.size(); ++i) {
       Monitor* monitor = new Monitor();
       monitor->set_bounds(new_monitors[i]->bounds());
       monitors_.push_back(monitor);
       NotifyMonitorAdded(monitor);
     }
   } else {
-    // Monitors are removed.
-    while (monitors_.size() > new_monitors.size()) {
+    // Monitors are removed. We keep the monitor for the primary
+    // monitor (at index 0) because it needs the monitor information
+    // even if it doesn't exit.
+    while (monitors_.size() > new_monitors.size() && monitors_.size() > 1) {
       Monitor* monitor = monitors_.back();
       // Monitor object is deleted in OnWindowDestroying.
       NotifyMonitorRemoved(monitor);
+      DCHECK(find(monitors_.begin(), monitors_.end(), monitor) ==
+             monitors_.end());
     }
   }
 }
 
 RootWindow* MultiMonitorManager::CreateRootWindowForMonitor(
     Monitor* monitor) {
   RootWindow* root_window = new RootWindow(monitor->bounds());
   root_window->AddObserver(this);
   root_window->AddRootWindowObserver(this);
   root_window->SetProperty(kMonitorKey, monitor);
@@ skipping 91 matching lines @@
          iter != monitors_.end(); ++iter)
       new_monitors.push_back(Copy(*iter));
     new_monitors.push_back(Copy(monitors_.front()));
     OnNativeMonitorsChanged(new_monitors);
     STLDeleteContainerPointers(new_monitors.begin(), new_monitors.end());
   }
 }
 
 }  // namespace internal
 }  // namespace ash