Add a SetDoNotFragment() method to DatagramSocket, and call this for

net/udp/datagram_socket.h

Index: net/udp/datagram_socket.h
diff --git a/net/udp/datagram_socket.h b/net/udp/datagram_socket.h
index f0e9fa10baa7fb181b9b2cc6810459c6c31359d6..cde1fd86506e0c96b964e8c137eee8858e3991c8 100644
--- a/net/udp/datagram_socket.h
+++ b/net/udp/datagram_socket.h
@@ -34,6 +34,11 @@ class NET_EXPORT_PRIVATE DatagramSocket {
   // (similar to getsockname)
   virtual int GetLocalAddress(IPEndPoint* address) const = 0;
 
+  // If supported by the platform, configures the socket to set the DF
+  // (Do not Fragment) bit on packets, which prevents routers from fragmenting
+  // them. Also, for IPv6, it prevents hosts from fragmenting them.

[mmenke, 2016/08/12 19:46:05]

hosts -> remote endpoint (Note that this is used for both server and client
sockets)

[mmenke, 2016/08/12 19:46:05]

Mention the return value, and if the socket is still usable on error.  And
whether it can be ERR_IO_PENDING (Which I assume it can't be)

[Ryan Hamilton, 2016/08/12 21:46:02]

Done.

+  virtual int SetDoNotFragment() = 0;
+
   // Gets the NetLog for this socket.
   virtual const BoundNetLog& NetLog() const = 0;
 };