Add a libfuzzer for RtpHeaderParser.

webrtc/test/fuzzers/rtp_header_fuzzer.cc

+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <bitset>
+
+#include "webrtc/modules/rtp_rtcp/source/rtp_packet_received.h"
+#include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
+#include "webrtc/modules/rtp_rtcp/source/rtp_utility.h"
+
+namespace webrtc {
+void FuzzOneInput(const uint8_t* data, size_t size) {
+  if (size <= 1)
+    return;
+
+  // We decide which header extensions to register by reading one byte
+  // from the beginning of |data| and interpreting it as a bitmask
+  // over the RTPExtensionType enum. That byte shouldn't also be part
+  // of the packet, so we adjust |data| and |size| to remove it.
+  std::bitset<8> extensionMask(data[0]);
+  data++;
+  size--;
+
+  RtpPacketReceived::ExtensionManager extensions;
+  for (int i = 1; i <= kRtpExtensionNumberOfExtensions; i++) {
+    // Skip i=0 which is kRtpExtensionNone i.e. not an actual extension.
+    if (extensionMask[i]) {
+      // We use i as the ID; it's used in negotiation so not relevant.
+      extensions.Register(static_cast<RTPExtensionType>(i), i);
+    }
+  }
+
+  RTPHeader rtp_header;
+  RtpUtility::RtpHeaderParser rtp_parser(data, size);
+  rtp_parser.Parse(&rtp_header, &extensions);
+}
+}  // namespace webrtc