NULL check before calling thumbnail_db_ method.

chrome/browser/history/history_backend.cc

Index: chrome/browser/history/history_backend.cc
diff --git a/chrome/browser/history/history_backend.cc b/chrome/browser/history/history_backend.cc
index 83a2afddf4b04becf4bfd5a32c1a92a7364f3c40..4e69a4bf9a666564457bf646e6814bda9bb01c89 100644
--- a/chrome/browser/history/history_backend.cc
+++ b/chrome/browser/history/history_backend.cc
@@ -659,7 +659,8 @@ void HistoryBackend::InitImpl(const std::string& languages) {
   if (base::RandInt(1, 100) == 50) {
     // Only do this computation sometimes since it can be expensive.
     db_->ComputeDatabaseMetrics(history_name);
-    thumbnail_db_->ComputeDatabaseMetrics();
+    if (thumbnail_db_)
+      thumbnail_db_->ComputeDatabaseMetrics();
   }
 
   // Tell the expiration module about all the nice databases we made. This must