Add some NULL-checks for ExtensionHost::extension to fix a crash bug.

chrome/browser/extensions/extension_host.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/extensions/extension_host.h"
 
 #include <list>
 
 #include "base/bind.h"
 #include "base/memory/singleton.h"
@@ skipping 141 matching lines @@
   render_view_host_ = host_contents_->GetRenderViewHost();
 
   // Listen for when an extension is unloaded from the same profile, as it may
   // be the same extension that this points to.
   registrar_.Add(this, chrome::NOTIFICATION_EXTENSION_UNLOADED,
                  content::Source<Profile>(profile_));
 }
 
 ExtensionHost::~ExtensionHost() {
   if (extension_host_type_ == chrome::VIEW_TYPE_EXTENSION_BACKGROUND_PAGE &&
-      extension_->has_lazy_background_page()) {
+      extension_ && extension_->has_lazy_background_page()) {
     UMA_HISTOGRAM_LONG_TIMES("Extensions.EventPageActiveTime",
                              since_created_.Elapsed());
   }
   content::NotificationService::current()->Notify(
       chrome::NOTIFICATION_EXTENSION_HOST_DESTROYED,
       content::Source<Profile>(profile_),
       content::Details<ExtensionHost>(this));
   ProcessCreationQueue::GetInstance()->Remove(this);
 }
 
@@ skipping 170 matching lines @@
       extension_host_type_ == chrome::VIEW_TYPE_EXTENSION_DIALOG ||
       extension_host_type_ == chrome::VIEW_TYPE_EXTENSION_INFOBAR ||
       extension_host_type_ == chrome::VIEW_TYPE_PANEL) {
 #if defined(TOOLKIT_VIEWS) || defined(OS_MACOSX)
     if (view())
       view()->DidStopLoading();
 #endif
   }
   if (notify) {
     if (extension_host_type_ == chrome::VIEW_TYPE_EXTENSION_BACKGROUND_PAGE) {
-      if (extension_->has_lazy_background_page()) {
+      if (extension_ && extension_->has_lazy_background_page()) {
         UMA_HISTOGRAM_TIMES("Extensions.EventPageLoadTime",
                             since_created_.Elapsed());
       } else {
         UMA_HISTOGRAM_TIMES("Extensions.BackgroundPageLoadTime",
                             since_created_.Elapsed());
       }
     } else if (extension_host_type_ == chrome::VIEW_TYPE_EXTENSION_DIALOG) {
       UMA_HISTOGRAM_TIMES("Extensions.DialogLoadTime",
                           since_created_.Elapsed());
     } else if (extension_host_type_ == chrome::VIEW_TYPE_EXTENSION_POPUP) {
@@ skipping 236 matching lines @@
   params.user_gesture = user_gesture;
   browser::Navigate(&params);
 }
 
 void ExtensionHost::RenderViewReady() {
   content::NotificationService::current()->Notify(
       chrome::NOTIFICATION_EXTENSION_HOST_CREATED,
       content::Source<Profile>(profile_),
       content::Details<ExtensionHost>(this));
 }