Enable database logging on history thread.

base/thread.cc

Index: base/thread.cc
===================================================================
--- base/thread.cc	(revision 25477)
+++ base/thread.cc	(working copy)
@@ -135,6 +135,10 @@
   message_loop_->PostTask(FROM_HERE, new ThreadQuitTask());
 }
 
+void Thread::Run(MessageLoop* message_loop) {
+  message_loop->Run();
+}
+
 void Thread::ThreadMain() {
   // The message loop for this thread.
   MessageLoop message_loop(startup_data_->options.message_loop_type);
@@ -153,7 +157,7 @@
   // startup_data_ can't be touched anymore since the starting thread is now
   // unlocked.
 
-  message_loop.Run();
+  Run(message_loop_);
 
   // Let the thread do extra cleanup.
   CleanUp();