net: Make UploadDataStream::Init() asynchronous.

net/http/http_network_transaction.cc

Index: net/http/http_network_transaction.cc
diff --git a/net/http/http_network_transaction.cc b/net/http/http_network_transaction.cc
index f0595baa0d753d032582fb8aee8858ca788463d4..d7ca1dc36d13490b78b0029c5a6b3ff3c33e1c54 100644
--- a/net/http/http_network_transaction.cc
+++ b/net/http/http_network_transaction.cc
@@ -19,6 +19,7 @@
 #include "base/string_number_conversions.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
+#include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 #include "googleurl/src/gurl.h"
 #include "net/base/auth.h"
@@ -733,7 +734,9 @@ int HttpNetworkTransaction::DoBuildRequest() {
   request_body_.reset(NULL);
   if (request_->upload_data) {
     request_body_.reset(new UploadDataStream(request_->upload_data));
-    const int error_code = request_body_->Init();
+    // InitSync() performs file IO. crbug.com/113669.
+    base::ThreadRestrictions::ScopedAllowIO allow_io;
+    const int error_code = request_body_->InitSync();
     if (error_code != OK) {
       request_body_.reset(NULL);
       return error_code;