Move RTCP histograms from vie_channel to video channel stats proxies.

webrtc/common_types.h

Index: webrtc/common_types.h
diff --git a/webrtc/common_types.h b/webrtc/common_types.h
index 8de1659364859baeb5352f144d33eefa81bd6784..d41887ffd2f1438f70a6d90e1695805c15c13358 100644
--- a/webrtc/common_types.h
+++ b/webrtc/common_types.h
@@ -211,6 +211,21 @@ struct RtcpPacketTypeCounter {
     }
   }
 
+  RtcpPacketTypeCounter Subtract(const RtcpPacketTypeCounter& other) const {
+    RtcpPacketTypeCounter diff = other;
+    diff.nack_packets -= nack_packets;
+    diff.fir_packets -= fir_packets;
+    diff.pli_packets -= pli_packets;
+    diff.nack_requests -= nack_requests;
+    diff.unique_nack_requests -= unique_nack_requests;
+    if (diff.first_packet_time_ms != -1 &&
+        diff.first_packet_time_ms < first_packet_time_ms) {
+      // Use youngest time.
+      diff.first_packet_time_ms = first_packet_time_ms;
+    }
+    return diff;
+  }
+
   int64_t TimeSinceFirstPacketInMs(int64_t now_ms) const {
     return (first_packet_time_ms == -1) ? -1 : (now_ms - first_packet_time_ms);
   }