net: Make UploadDataStream::Init() asynchronous.

net/base/upload_element_reader.h

Index: net/base/upload_element_reader.h
diff --git a/net/base/upload_element_reader.h b/net/base/upload_element_reader.h
index 3e8bceab90f7cc3ad4ffff24828c091b1c432bba..5af2e23f7abe27b980a5ac3463dcc7fbb76b3307 100644
--- a/net/base/upload_element_reader.h
+++ b/net/base/upload_element_reader.h
@@ -6,6 +6,7 @@
 #define NET_BASE_UPLOAD_ELEMENT_READER_H_
 
 #include "base/basictypes.h"
+#include "net/base/completion_callback.h"
 #include "net/base/net_export.h"
 
 namespace net {
@@ -21,7 +22,12 @@ class NET_EXPORT UploadElementReader {
   // Creates an appropriate UploadElementReader instance for the given element.
   static UploadElementReader* Create(const UploadElement& element);
 
-  // Initializes the instance synchronously.
+  // Initializes the instance synchronously when possible, otherwise does
+  // initialization aynschronously, returns ERR_IO_PENDING and runs callback.
+  virtual int Init(const CompletionCallback& callback) = 0;
+
+  // Initializes the instance always synchronously.
+  // Use this method only in tests and Chrome Frame.
   virtual int InitSync() = 0;
 
   // Returns the byte-length of the element.  For files that do not exist, 0