Split up quic_frames.{h,cc} into files for each frame type.

net/quic/core/frames/quic_mtu_discovery_frame.h

Index: net/quic/core/frames/quic_mtu_discovery_frame.h
diff --git a/net/quic/core/frames/quic_mtu_discovery_frame.h b/net/quic/core/frames/quic_mtu_discovery_frame.h
new file mode 100644
index 0000000000000000000000000000000000000000..2395a665f4e7ac0046e897750994eccd18f803fc
--- /dev/null
+++ b/net/quic/core/frames/quic_mtu_discovery_frame.h
@@ -0,0 +1,18 @@
+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_QUIC_CORE_FRAMES_QUIC_MTU_DISCOVERY_FRAME_H_
+#define NET_QUIC_CORE_FRAMES_QUIC_MTU_DISCOVERY_FRAME_H_
+
+#include "net/base/net_export.h"
+
+namespace net {
+
+// A path MTU discovery frame contains no payload and is serialized as a ping
+// frame.
+struct NET_EXPORT_PRIVATE QuicMtuDiscoveryFrame {};
+
+}  // namespace net
+
+#endif  // NET_QUIC_CORE_FRAMES_QUIC_MTU_DISCOVERY_FRAME_H_