Fix parsing padding byte in rtp header extension

BUG=chromium:664598

Review-Url: https://codereview.webrtc.org/2498903003
Cr-Commit-Position: refs/heads/master@{#15230}
diff --git a/webrtc/modules/BUILD.gn b/webrtc/modules/BUILD.gn
index 5537829..0996098 100644
--- a/webrtc/modules/BUILD.gn
+++ b/webrtc/modules/BUILD.gn
@@ -473,6 +473,7 @@
       "rtp_rtcp/source/rtp_payload_registry_unittest.cc",
       "rtp_rtcp/source/rtp_rtcp_impl_unittest.cc",
       "rtp_rtcp/source/rtp_sender_unittest.cc",
+      "rtp_rtcp/source/rtp_utility_unittest.cc",
       "rtp_rtcp/source/time_util_unittest.cc",
       "rtp_rtcp/source/ulpfec_generator_unittest.cc",
       "rtp_rtcp/source/ulpfec_header_reader_writer_unittest.cc",