net: Make UploadDataStream::Init() asynchronous.

net/base/upload_element_reader.cc

Index: net/base/upload_element_reader.cc
diff --git a/net/base/upload_element_reader.cc b/net/base/upload_element_reader.cc
index bb5cd85900c4418d5eedc61d3b623af91aa2b706..a7f25f6ac154284bee97f309e93baac7c01ef4c3 100644
--- a/net/base/upload_element_reader.cc
+++ b/net/base/upload_element_reader.cc
@@ -5,6 +5,7 @@
 #include "net/base/upload_element_reader.h"
 
 #include "base/logging.h"
+#include "net/base/net_errors.h"
 #include "net/base/upload_bytes_element_reader.h"
 #include "net/base/upload_element.h"
 #include "net/base/upload_file_element_reader.h"
@@ -31,6 +32,11 @@ UploadElementReader* UploadElementReader::Create(const UploadElement& element) {
   return reader;
 }
 
+int UploadElementReader::InitSync() {
+  NOTREACHED() << "This instance does not support InitSync().";
+  return ERR_NOT_IMPLEMENTED;
+}
+
 bool UploadElementReader::IsInMemory() const {
   return false;
 }