Have content/ create and destroy its own threads.

content/shell/shell_browser_context.cc

Index: content/shell/shell_browser_context.cc
diff --git a/content/shell/shell_browser_context.cc b/content/shell/shell_browser_context.cc
index 0f75d89138a01b152b1261bb9401d608722fa694..f011b32ba7bf466f8aedf98eeb466a164b524862 100644
--- a/content/shell/shell_browser_context.cc
+++ b/content/shell/shell_browser_context.cc
@@ -8,6 +8,7 @@
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/path_service.h"
+#include "base/threading/thread.h"
 #include "content/browser/appcache/chrome_appcache_service.h"
 #include "content/browser/chrome_blob_storage_context.h"
 #include "content/browser/download/download_id_factory.h"
@@ -140,8 +141,10 @@ net::URLRequestContextGetter* ShellBrowserContext::GetRequestContext()  {
   if (!url_request_getter_) {
     url_request_getter_ = new ShellURLRequestContextGetter(
         GetPath(),
-        shell_main_parts_->io_thread()->message_loop(),
-        shell_main_parts_->file_thread()->message_loop());
+        BrowserThread::UnsafeGetBrowserThread(
+            BrowserThread::IO)->message_loop(),
+        BrowserThread::UnsafeGetBrowserThread(
+            BrowserThread::FILE)->message_loop());
   }
   return url_request_getter_;
 }