net: Make UploadData::GetContentLength() asynchronous.

content/browser/renderer_host/resource_dispatcher_host.cc

Index: content/browser/renderer_host/resource_dispatcher_host.cc
diff --git a/content/browser/renderer_host/resource_dispatcher_host.cc b/content/browser/renderer_host/resource_dispatcher_host.cc
index b925a8563fadf673bf774e5b078223c4c3fd6318..635cbefec8fa395fac5a2fddde97eea463b09a59 100644
--- a/content/browser/renderer_host/resource_dispatcher_host.cc
+++ b/content/browser/renderer_host/resource_dispatcher_host.cc
@@ -21,6 +21,7 @@
 #include "base/shared_memory.h"
 #include "base/stl_util.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
+#include "base/threading/thread_restrictions.h"
 #include "content/browser/appcache/chrome_appcache_service.h"
 #include "content/browser/cert_store.h"
 #include "content/browser/child_process_security_policy_impl.h"
@@ -647,7 +648,8 @@ void ResourceDispatcherHost::BeginRequest(
   if (request_data.upload_data) {
     request->set_upload(request_data.upload_data);
     // This results in performing file IO. crbug.com/112607.
-    upload_size = request_data.upload_data->GetContentLength();
+    base::ThreadRestrictions::ScopedAllowIO allow_io;
+    upload_size = request_data.upload_data->GetContentLengthSync();
   }
 
   // Install a CrossSiteResourceHandler if this request is coming from a