Have content/ create and destroy its own threads.

content/browser/browser_process_sub_thread.cc

Index: content/browser/browser_process_sub_thread.cc
diff --git a/content/browser/browser_process_sub_thread.cc b/content/browser/browser_process_sub_thread.cc
index 31c129e1589135207f12b10df417506cc8e53834..7c77d7e0b47b66af3407aa236d679a51e1ccfb83 100644
--- a/content/browser/browser_process_sub_thread.cc
+++ b/content/browser/browser_process_sub_thread.cc
@@ -17,8 +17,6 @@ BrowserProcessSubThread::BrowserProcessSubThread(BrowserThread::ID identifier)
     : BrowserThreadImpl(identifier) {}
 
 BrowserProcessSubThread::~BrowserProcessSubThread() {
-  // We cannot rely on our base class to stop the thread since we want our
-  // CleanUp function to run.
   Stop();
 }
 
@@ -29,9 +27,13 @@ void BrowserProcessSubThread::Init() {
 #endif
 
   notification_service_ = new NotificationServiceImpl;
+
+  BrowserThreadImpl::Init();
 }
 
 void BrowserProcessSubThread::CleanUp() {
+  BrowserThreadImpl::CleanUp();
+
   delete notification_service_;
   notification_service_ = NULL;