Remove QUIC_VERSION_15 now that Chrome Stable supports QUIC_VERSION_16.

net/quic/test_tools/quic_connection_peer.cc

Index: net/quic/test_tools/quic_connection_peer.cc
diff --git a/net/quic/test_tools/quic_connection_peer.cc b/net/quic/test_tools/quic_connection_peer.cc
index c4c63c7bc30b92780f2ef39baace65cf6364bcae..6847c1d91f8992635635b78686c5c8ea4f321db6 100644
--- a/net/quic/test_tools/quic_connection_peer.cc
+++ b/net/quic/test_tools/quic_connection_peer.cc
@@ -43,6 +43,12 @@ QuicAckFrame* QuicConnectionPeer::CreateAckFrame(QuicConnection* connection) {
 }
 
 // static
+QuicStopWaitingFrame* QuicConnectionPeer::CreateStopWaitingFrame(
+    QuicConnection* connection) {
+  return connection->CreateStopWaitingFrame();
+}
+
+// static
 QuicConnectionVisitorInterface* QuicConnectionPeer::GetVisitor(
     QuicConnection* connection) {
   return connection->visitor_;