Remove QUIC_VERSION_15 now that Chrome Stable supports QUIC_VERSION_16.

net/quic/quic_protocol.cc

Index: net/quic/quic_protocol.cc
diff --git a/net/quic/quic_protocol.cc b/net/quic/quic_protocol.cc
index f0b8b68966766a90948362852591b9aaa5001236..87c9cd91b1197b841057cd43ae2f698f51fb1c06 100644
--- a/net/quic/quic_protocol.cc
+++ b/net/quic/quic_protocol.cc
@@ -159,8 +159,6 @@ QuicVersionVector QuicSupportedVersions() {
 
 QuicTag QuicVersionToQuicTag(const QuicVersion version) {
   switch (version) {
-    case QUIC_VERSION_15:
-      return MakeQuicTag('Q', '0', '1', '5');
     case QUIC_VERSION_16:
       return MakeQuicTag('Q', '0', '1', '6');
     case QUIC_VERSION_18:
@@ -197,7 +195,6 @@ return #x
 
 string QuicVersionToString(const QuicVersion version) {
   switch (version) {
-    RETURN_STRING_LITERAL(QUIC_VERSION_15);
     RETURN_STRING_LITERAL(QUIC_VERSION_16);
     RETURN_STRING_LITERAL(QUIC_VERSION_18);
     RETURN_STRING_LITERAL(QUIC_VERSION_19);
@@ -502,8 +499,7 @@ ostream& operator<<(ostream& os, const QuicStreamFrame& stream_frame) {
 }
 
 ostream& operator<<(ostream& os, const QuicAckFrame& ack_frame) {
-  os << "sent info { " << ack_frame.sent_info << " } "
-     << "received info { " << ack_frame.received_info << " }\n";
+  os << "received info { " << ack_frame.received_info << " }\n";
   return os;
 }