MessageLoop: wire the unused static method in base::Thread (follow-up cleanup)

Actually use the private static method (CreateUnbound) in base::Thread.

I added the method in the last refactoring patch but forgot to use it;
I can either remove the static method or use it, I do the latter in this
patch as I thought leaving the private ctor of MessageLoop only for
delegated use-case cleaner.

BUG=465458
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/1212193003

Cr-Commit-Position: refs/heads/master@{#336710}


CrOS-Libchrome-Original-Commit: 547a48bb006e275f1192c983a634e911c8c1edbd
diff --git a/base/message_loop/message_loop.h b/base/message_loop/message_loop.h
index b1b219a..1b6d407 100644
--- a/base/message_loop/message_loop.h
+++ b/base/message_loop/message_loop.h
@@ -415,7 +415,7 @@
   // thread the message loop runs on, before calling Run().
   // Before BindToCurrentThread() is called only Post*Task() functions can
   // be called on the message loop.
-  scoped_ptr<MessageLoop> CreateUnbound(
+  static scoped_ptr<MessageLoop> CreateUnbound(
       Type type,
       MessagePumpFactoryCallback pump_factory);
 
diff --git a/base/threading/thread.cc b/base/threading/thread.cc
index 6ca1cae..7bff242 100644
--- a/base/threading/thread.cc
+++ b/base/threading/thread.cc
@@ -94,8 +94,9 @@
     type = MessageLoop::TYPE_CUSTOM;
 
   message_loop_timer_slack_ = options.timer_slack;
-  message_loop_ = new MessageLoop(type, options.message_pump_factory);
-
+  scoped_ptr<MessageLoop> message_loop = MessageLoop::CreateUnbound(
+      type, options.message_pump_factory);
+  message_loop_ = message_loop.get();
   start_event_.reset(new WaitableEvent(false, false));
 
   // Hold the thread_lock_ while starting a new thread, so that we can make sure
@@ -111,13 +112,16 @@
     }
     if (!created) {
       DLOG(ERROR) << "failed to create thread";
-      delete message_loop_;
       message_loop_ = nullptr;
       start_event_.reset();
       return false;
     }
   }
 
+  // The ownership of message_loop is managemed by the newly created thread
+  // within the ThreadMain.
+  ignore_result(message_loop.release());
+
   DCHECK(message_loop_);
   return true;
 }