Partially revert r53873 (and the valgrind suppression for it).

chrome/browser/dom_ui/dom_ui_thumbnail_source.cc

 // Copyright (c) 2010 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/dom_ui/dom_ui_thumbnail_source.h"
 
 #include "app/resource_bundle.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "chrome/browser/profile.h"
 #include "chrome/browser/history/top_sites.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/notification_service.h"
 #include "chrome/common/url_constants.h"
 #include "gfx/codec/jpeg_codec.h"
 #include "googleurl/src/gurl.h"
 #include "grit/theme_resources.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 
 DOMUIThumbnailSource::DOMUIThumbnailSource(Profile* profile)
     : DataSource(chrome::kChromeUIThumbnailPath, MessageLoop::current()),
       profile_(profile) {
 }
 
 DOMUIThumbnailSource::~DOMUIThumbnailSource() {
-  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
 }
 
 void DOMUIThumbnailSource::StartDataRequest(const std::string& path,
                                             bool is_off_the_record,
                                             int request_id) {
-  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kTopSites)) {
     scoped_refptr<history::TopSites> top_sites = profile_->GetTopSites();
     RefCountedBytes* data = NULL;
     if (top_sites->GetPageThumbnail(GURL(path), &data)) {
       // We have the thumbnail.
       SendResponse(request_id, data);
     } else {
       SendDefaultThumbnail(request_id);
     }
     return;
@@ skipping 25 matching lines @@
     default_thumbnail_ =
         ResourceBundle::GetSharedInstance().LoadDataResourceBytes(
             IDR_DEFAULT_THUMBNAIL);
   }
   SendResponse(request_id, default_thumbnail_);
 }
 
 void DOMUIThumbnailSource::OnThumbnailDataAvailable(
     HistoryService::Handle request_handle,
     scoped_refptr<RefCountedBytes> data) {
-  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
   HistoryService* hs =
       profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
   int request_id = cancelable_consumer_.GetClientData(hs, request_handle);
   // Forward the data along to the networking system.
   if (data.get() && !data->data.empty()) {
     SendResponse(request_id, data);
   } else {
     SendDefaultThumbnail(request_id);
   }
 }