Update the current RTP parser fuzzer to handle header extensions.

webrtc/test/fuzzers/rtp_header_fuzzer.cc

Index: webrtc/test/fuzzers/rtp_header_fuzzer.cc
diff --git a/webrtc/test/fuzzers/rtp_header_fuzzer.cc b/webrtc/test/fuzzers/rtp_header_fuzzer.cc
index fcc737728cffb72a9eca0d1d3b040276107ed5f2..914a8fb9494bc2e701d658ec5c1e55414b6a0586 100644
--- a/webrtc/test/fuzzers/rtp_header_fuzzer.cc
+++ b/webrtc/test/fuzzers/rtp_header_fuzzer.cc
@@ -10,29 +10,35 @@
 
 #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_packet_received.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_utility.h"
 
 namespace webrtc {
+// 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. This assert ensures one byte is enough.
+static_assert(kRtpExtensionNumberOfExtensions <= 8,
+              "Insufficient bits read to configure all header extensions. Add "
+              "an extra byte and update the switches.");
+
 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.
+  // Don't use the configuration byte as part of the packet.
   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);
+  for (int i = 0; i < kRtpExtensionNumberOfExtensions; i++) {
+    RTPExtensionType extension_type = static_cast<RTPExtensionType>(i);
+    if (extensionMask[i] && extension_type != kRtpExtensionNone) {
+      // Extensions are registered with an ID, which you signal to the
+      // peer so they know what to expect. This code only cares about
+      // parsing so the value of the ID isn't relevant; we use i.
+      extensions.Register(extension_type, i);
     }
   }