Fix packetization logic to leave space for extensions in the last packet

webrtc/modules/rtp_rtcp/BUILD.gn

Index: webrtc/modules/rtp_rtcp/BUILD.gn
diff --git a/webrtc/modules/rtp_rtcp/BUILD.gn b/webrtc/modules/rtp_rtcp/BUILD.gn
index 5d754d9974b7ce3a1116090518be36dd7366c1da..6a459d1f28851beb797f36e61c6bf89aa3c743a6 100644
--- a/webrtc/modules/rtp_rtcp/BUILD.gn
+++ b/webrtc/modules/rtp_rtcp/BUILD.gn
@@ -150,8 +150,6 @@ rtc_static_library("rtp_rtcp") {
     "source/ulpfec_receiver_impl.cc",
     "source/ulpfec_receiver_impl.h",
     "source/video_codec_information.h",
-    "source/vp8_partition_aggregator.cc",
-    "source/vp8_partition_aggregator.h",
   ]
 
   if (rtc_enable_bwe_test_logging) {
@@ -312,6 +310,7 @@ if (rtc_include_tests) {
       "source/rtcp_sender_unittest.cc",
       "source/rtp_fec_unittest.cc",
       "source/rtp_format_h264_unittest.cc",
+      "source/rtp_format_video_generic_unittest.cc",
       "source/rtp_format_vp8_test_helper.cc",
       "source/rtp_format_vp8_test_helper.h",
       "source/rtp_format_vp8_unittest.cc",
@@ -328,7 +327,6 @@ if (rtc_include_tests) {
       "source/ulpfec_generator_unittest.cc",
       "source/ulpfec_header_reader_writer_unittest.cc",
       "source/ulpfec_receiver_unittest.cc",
-      "source/vp8_partition_aggregator_unittest.cc",
       "test/testAPI/test_api.cc",
       "test/testAPI/test_api.h",
       "test/testAPI/test_api_audio.cc",