Reduce/remove usage of BrowserThread in content/browser/loader.

content/browser/browser_main_loop.cc

Index: content/browser/browser_main_loop.cc
diff --git a/content/browser/browser_main_loop.cc b/content/browser/browser_main_loop.cc
index ba276a6acc07aa22fcc09a95cd89497fa8814223..d77edf75c5bfd64043222ff5d36f7ec3f3a49938 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -1487,8 +1487,13 @@ int BrowserMainLoop::BrowserThreadsStarted() {
     // intercept requests to create handlers for download requests. We need to
     // find a better way to achieve this. Ideally we don't want knowledge of
     // downloads in ResourceDispatcherHostImpl.
+    // We pass the task runners for the UI and IO threads as a stopgap approach
+    // for now. Eventually variants of these runners would be available in the
+    // network service.
     resource_dispatcher_host_.reset(new ResourceDispatcherHostImpl(
-        base::Bind(&DownloadResourceHandler::Create)));
+        base::Bind(&DownloadResourceHandler::Create),
+        BrowserThread::GetTaskRunnerForThread(BrowserThread::UI),
+        BrowserThread::GetTaskRunnerForThread(BrowserThread::IO)));
     GetContentClient()->browser()->ResourceDispatcherHostCreated();
 
     loader_delegate_.reset(new LoaderDelegateImpl());