Implement video frame acknowledgements in the chromoting protocol.

remoting/proto/video.proto

Index: remoting/proto/video.proto
diff --git a/remoting/proto/video.proto b/remoting/proto/video.proto
index 0ee29c9b8922d65c30dfb653fa32db538104eb79..b88c2244811d74875b1c496893562b7532311093 100644
--- a/remoting/proto/video.proto
+++ b/remoting/proto/video.proto
@@ -66,4 +66,18 @@ message VideoPacket {
 
   // Optional frame timestamp. Used in tests to estimate frame latency.
   optional int64 timestamp = 12;
+
+  optional int32 frame_id = 13;
+}
+
+message VideoAck {
+  // Frame ID.
+  optional int32 frame_id = 1;
+
+  // Time in microseconds it took to receive the VideoPacket from the beginning
+  // to the end. Can be 0 for small packets.
+  optional int32 time_to_receive_us = 2;
+
+  // Time in microseconds it took to render the frame.
+  optional int32 rendering_delay_us = 3;
 }