Linux: fix a bunch of NULL vs. 0 issues spotted by gcc 4.5.

chrome/browser/history/top_sites.cc

 // Copyright (c) 2011 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/history/top_sites.h"
 
 #include <algorithm>
 #include <set>
 
 #include "app/l10n_util.h"
@@ skipping 425 matching lines @@
   for (std::map<GURL, size_t>::const_iterator i = all_old_urls.begin();
        i != all_old_urls.end(); ++i) {
     if (i->second != kAlreadyFoundMarker)
       delta->deleted.push_back(old_list[i->second]);
   }
 }
 
 CancelableRequestProvider::Handle TopSites::StartQueryForMostVisited() {
   DCHECK(loaded_);
   if (!profile_)
-    return NULL;
+    return 0;
 
   HistoryService* hs = profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
   // |hs| may be null during unit tests.
   if (hs) {
     return hs->QueryMostVisitedURLs(
         num_results_to_request_from_history(),
         kDaysOfHistory,
         &cancelable_consumer_,
         NewCallback(this, &TopSites::OnTopSitesAvailableFromHistory));
   }
-  return NULL;
+  return 0;
 }
 
 TopSites::~TopSites() {
 }
 
 bool TopSites::SetPageThumbnailNoDB(const GURL& url,
                                     const RefCountedBytes* thumbnail_data,
                                     const ThumbnailScore& score) {
   // This should only be invoked when we know about the url.
   DCHECK(cache_->IsKnownURL(url));
@@ skipping 442 matching lines @@
   SetTopSites(pages);
 
   // Used only in testing.
   NotificationService::current()->Notify(
       NotificationType::TOP_SITES_UPDATED,
       Source<TopSites>(this),
       Details<CancelableRequestProvider::Handle>(&handle));
 }
 
 }  // namespace history