Mojo UDP API implementation.

mojo/services/public/interfaces/network/udp_socket.mojom

Index: mojo/services/public/interfaces/network/udp_socket.mojom
diff --git a/mojo/services/public/interfaces/network/udp_socket.mojom b/mojo/services/public/interfaces/network/udp_socket.mojom
index 6f0cff3efe324a30aa8abca656222b3915c3b920..33e4118e5af8203a5993dba7fa5139ccbc861272 100644
--- a/mojo/services/public/interfaces/network/udp_socket.mojom
+++ b/mojo/services/public/interfaces/network/udp_socket.mojom
@@ -63,11 +63,18 @@ interface UDPSocket {
   SendToAndForget(NetAddress addr, uint8[] data);
 
   // Sends data to the specified destination. The socket must be bound.
+  // On success, |result.code| is a non-negative number indicating how many
+  // bytes have been written. Otherwise, it is a network error code, including
+  // (but not limited to):
+  // - ERR_INSUFFICIENT_RESOURCES (-12): The service doesn't have sufficient
+  //   resource to complete the operation. One possible cause is that the client
+  //   tries to send too many packets in a short period of time.
   SendTo(NetAddress addr, uint8[] data) => (NetworkError result);
 };
 
 interface UDPSocketClient {
-  // |addr| and |data| are non-NULL on success.
+  // On success, |addr| and |data| are non-NULL, |result.code| is a non-negative
+  // number indicating how many bytes have been received.
   OnReceived(NetworkError result, NetAddress? addr, uint8[]? data);
 };