Clean up dns prefetch code, and also port it.

chrome/browser/browser_process_impl.cc

Index: chrome/browser/browser_process_impl.cc
diff --git a/chrome/browser/browser_process_impl.cc b/chrome/browser/browser_process_impl.cc
index ee110667d7e6960449a1fa1ca72b232d401707a0..37feb2376d5cbc344c5038c623d95bf0cc011194 100644
--- a/chrome/browser/browser_process_impl.cc
+++ b/chrome/browser/browser_process_impl.cc
@@ -13,6 +13,7 @@
 #include "chrome/browser/debugger/debugger_wrapper.h"
 #include "chrome/browser/google_url_tracker.h"
 #include "chrome/browser/metrics/metrics_service.h"
+#include "chrome/browser/net/dns_global.h"
 #include "chrome/browser/profile_manager.h"
 #include "chrome/browser/renderer_host/render_process_host.h"
 #include "chrome/browser/renderer_host/resource_dispatcher_host.h"
@@ -174,6 +175,11 @@ BrowserProcessImpl::~BrowserProcessImpl() {
     resource_dispatcher_host()->Shutdown();
   }
 
+  // Shutdown DNS prefetching now to ensure that network stack objects
+  // living on the IO thread get destroyed before the IO thread goes away.
+  io_thread_->message_loop()->PostTask(FROM_HERE,
+      NewRunnableFunction(chrome_browser_net::ShutdownDnsPrefetch));
+
   // Need to stop io_thread_ before resource_dispatcher_host_, since
   // io_thread_ may still deref ResourceDispatcherHost and handle resource
   // request before going away.