Add Socket::ReadIfReady()

net/socket/socket_posix.h

Index: net/socket/socket_posix.h
diff --git a/net/socket/socket_posix.h b/net/socket/socket_posix.h
index bf4b7e53d9b055793b3b6f6bb4bece7040268d2c..90f7f39956665527bd4a42cc603cf2cf2db67ef9 100644
--- a/net/socket/socket_posix.h
+++ b/net/socket/socket_posix.h
@@ -59,6 +59,14 @@ class NET_EXPORT_PRIVATE SocketPosix : public base::MessageLoopForIO::Watcher {
   // errno, though errno is set if read or write events happen with error.
   // TODO(byungchul): Need more robust way to pass system errno.
   int Read(IOBuffer* buf, int buf_len, const CompletionCallback& callback);
+
+  // Reads as much data as possible into |buf| without blocking. If read is to
+  // be retried later, |callback| will be invoked when data is ready for
+  // reading.
+  // See socket.h for more information.
+  int ReadIfReady(IOBuffer* buf,
+                  int buf_len,
+                  const CompletionCallback& callback);
   int Write(IOBuffer* buf, int buf_len, const CompletionCallback& callback);
 
   // Waits for next write event. This is called by TCPSocketPosix for TCP