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

chrome/browser/history/top_sites.cc

Index: chrome/browser/history/top_sites.cc
diff --git a/chrome/browser/history/top_sites.cc b/chrome/browser/history/top_sites.cc
index 16355230338593dad9680302702a82e8f1541f6a..a1c0a170ba128b27f416c80808b4ebdf4f60030a 100644
--- a/chrome/browser/history/top_sites.cc
+++ b/chrome/browser/history/top_sites.cc
@@ -443,7 +443,7 @@ void TopSites::DiffMostVisited(const MostVisitedURLList& old_list,
 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.
@@ -454,7 +454,7 @@ CancelableRequestProvider::Handle TopSites::StartQueryForMostVisited() {
         &cancelable_consumer_,
         NewCallback(this, &TopSites::OnTopSitesAvailableFromHistory));
   }
-  return NULL;
+  return 0;
 }
 
 TopSites::~TopSites() {