Avoid generating thumbnails while WebContents is destructed.

chrome/browser/ui/tab_contents/tab_contents.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/tab_contents/tab_contents.h"
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
 #include "chrome/browser/autofill/autocomplete_history_manager.h"
 #include "chrome/browser/autofill/autofill_external_delegate.h"
@@ skipping 189 matching lines @@
   // happens to be already connected.
 #if defined(ENABLE_ONE_CLICK_SIGNIN)
   if (OneClickSigninHelper::CanOffer(contents, "", false))
       one_click_signin_helper_.reset(new OneClickSigninHelper(contents));
 #endif
 }
 
 TabContents::~TabContents() {
   in_destructor_ = true;
 
-  // Need to reset |thumbnail_generator_| here before |web_contents_| is
-  // deleted because destructing |web_contents_| can end up causing the
-  // thumbnailer to generate a thumbnail. Since TabContents can be
-  // destructed during shutdown, trying to generate a thumbnail by sending an
-  // IPC message to the GPU process is not safe. Sending
-  // chrome::NOTIFICATION_TAB_CONTENTS_DESTROYED can also cause the thumbnailer

[mazda, 2012/08/30 17:19:18]

I was forgetting that we need to deal with this case. We want to avoid
generating thumbnails here, too. WebContents::IsBeingDestroyed cannot be used
for this case because it's before entering its dtor.
I wrote an idea to deal with this case in another comment.

[Avi (use Gerrit), 2012/08/30 18:16:26]

Note that NOTIFICATION_TAB_CONTENTS_DESTROYED is going away when I kill
TabContents.

[mazda, 2012/08/30 19:39:22]

That's a great. Then WebContents::IsBeingDestroyed can be used.

-  // to generate a thumbnail, so this must be placed before sending the
-  // notification.
-  thumbnail_generator_.reset();
-
   content::NotificationService::current()->Notify(
       chrome::NOTIFICATION_TAB_CONTENTS_DESTROYED,
       content::Source<TabContents>(this),
       content::NotificationService::NoDetails());
 
   // Need to tear down infobars before the WebContents goes away.
   // TODO(avi): Can we get this handled by the tab helper itself?
   infobar_tab_helper_.reset();
 }
 
@@ skipping 46 matching lines @@
 #if defined(ENABLE_SESSION_SERVICE)
   SessionService* session =
       SessionServiceFactory::GetForProfile(profile());
   if (session) {
     session->SetTabUserAgentOverride(restore_tab_helper()->window_id(),
                                      restore_tab_helper()->session_id(),
                                      user_agent);
   }
 #endif
 }