Fix SDP parsing crash due to missing track ID in "a=msid".

webrtc/pc/webrtcsdp_unittest.cc

Index: webrtc/pc/webrtcsdp_unittest.cc
diff --git a/webrtc/pc/webrtcsdp_unittest.cc b/webrtc/pc/webrtcsdp_unittest.cc
index 75116e8e33ec5ac5ec5276546ab65b78c0c9ee6f..1a6a212cdd9f0f1ad704088594e8e76cbc285575 100644
--- a/webrtc/pc/webrtcsdp_unittest.cc
+++ b/webrtc/pc/webrtcsdp_unittest.cc
@@ -3446,3 +3446,36 @@ TEST_F(WebRtcSdpTest, DeserializeInvalidPortInCandidateAttribute) {
   JsepSessionDescription jdesc_output(kDummyString);
   EXPECT_FALSE(SdpDeserialize(kSdpWithInvalidCandidatePort, &jdesc_output));
 }
+
+// Test that "a=msid" with a missing track ID is rejected and doesn't crash.
+// Regression test for:
+// https://bugs.chromium.org/p/chromium/issues/detail?id=686405
+TEST_F(WebRtcSdpTest, DeserializeMsidAttributeWithMissingTrackId) {
+  static const char kSdpWithMissingTrackId[] =
+      "v=0\r\n"
+      "o=- 18446744069414584320 18446462598732840960 IN IP4 127.0.0.1\r\n"
+      "s=-\r\n"
+      "t=0 0\r\n"
+      "m=audio 9 RTP/SAVPF 111\r\n"
+      "c=IN IP4 0.0.0.0\r\n"
+      "a=rtpmap:111 opus/48000/2\r\n"
+      "a=msid:stream_id \r\n";
+
+  JsepSessionDescription jdesc_output(kDummyString);
+  EXPECT_FALSE(SdpDeserialize(kSdpWithMissingTrackId, &jdesc_output));
+}
+
+TEST_F(WebRtcSdpTest, DeserializeMsidAttributeWithMissingStreamId) {
+  static const char kSdpWithMissingStreamId[] =
+      "v=0\r\n"
+      "o=- 18446744069414584320 18446462598732840960 IN IP4 127.0.0.1\r\n"
+      "s=-\r\n"
+      "t=0 0\r\n"
+      "m=audio 9 RTP/SAVPF 111\r\n"
+      "c=IN IP4 0.0.0.0\r\n"
+      "a=rtpmap:111 opus/48000/2\r\n"
+      "a=msid: track_id\r\n";
+
+  JsepSessionDescription jdesc_output(kDummyString);
+  EXPECT_FALSE(SdpDeserialize(kSdpWithMissingStreamId, &jdesc_output));
+}