Fix an ExtensionPopup crash on browser window close.

chrome/browser/ui/views/extensions/extension_popup.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/views/extensions/extension_popup.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/devtools/devtools_window.h"
@@ skipping 140 matching lines @@
   sz.set_height(std::max(kMinHeight, std::min(kMaxHeight, sz.height())));
   return sz;
 }
 
 void ExtensionPopup::OnWidgetDestroying(views::Widget* widget) {
   BubbleDelegateView::OnWidgetDestroying(widget);
 #if defined(USE_AURA)
   aura::Window* bubble_window = GetWidget()->GetNativeWindow();
   aura::client::ActivationClient* activation_client =
       aura::client::GetActivationClient(bubble_window->GetRootWindow());
-  activation_client->RemoveObserver(this);
+  // If the popup was being inspected with devtools and the browser window was
+  // closed, then the root window and activation client are already destroyed.
+  if (activation_client)
+    activation_client->RemoveObserver(this);
 #endif
 }
 
 void ExtensionPopup::OnWidgetActivationChanged(views::Widget* widget,
                                                bool active) {
   // Dismiss only if the window being activated is not owned by this popup's
   // window. In particular, don't dismiss when we lose activation to a child
   // dialog box. Possibly relevant: http://crbug.com/106723 and
   // http://crbug.com/179786
   views::Widget* this_widget = GetWidget();
@@ skipping 76 matching lines @@
   GetWidget()->Show();
 
   // Focus on the host contents when the bubble is first shown.
   host()->host_contents()->Focus();
 
   if (inspect_with_devtools_) {
     DevToolsWindow::OpenDevToolsWindow(host()->render_view_host(),
         DevToolsToggleAction::ShowConsole());
   }
 }