Predator and CL could not provide any possible suspects.
Using Code Search for the file, "webm_cluster_parser.cc" assigning to the concern owner who might be related.

@dalecurtis -- Could you please look into the issue, kindly re-assign if this is not related to your changes.
Thank You.

Likely duplicate of  Issue 764606  (same check, just MSAN rather than ASAN). 

This check is not a security concern, so reducing to P2. 

See also bug 271794.

Automatically applying components based on information from OWNERS files. If this seems incorrect, please apply the Test-Predator-Wrong-Components label.

Chris, I'm reassigning this to Thomas (along with suspected duplicate  bug 764606 .)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7ea9bee45009ccb9b5f4bdf5c86d43e8644f2556

commit 7ea9bee45009ccb9b5f4bdf5c86d43e8644f2556
Author: Thomas Guilbert <tguilbert@chromium.org>
Date: Wed Oct 04 03:38:29 2017

Fix int64 overflow in WebmClusterParser

If the value of |cluster_timecode_| and |timecode_multiplier_|
is big enough, we can end up with a value that does not fit in
an int64_t. This in turn means that all buffers will have kNoTimestamp
as a timestamp, which causes some CHECKs to fail later on.

Bug:  764606 ,  765627 
Change-Id: Ia11b19606a05c412390a597ae5a4ae5ccf2dab3c
Reviewed-on: https://chromium-review.googlesource.com/699522
Commit-Queue: Thomas Guilbert <tguilbert@chromium.org>
Reviewed-by: Matthew Wolenetz <wolenetz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506294}
[modify] https://crrev.com/7ea9bee45009ccb9b5f4bdf5c86d43e8644f2556/media/formats/webm/webm_cluster_parser.cc

ClusterFuzz has detected this issue as fixed in range 506278:506297.

Detailed report: https://clusterfuzz.com/testcase?key=6043553112522752

Fuzzer: libFuzzer_mediasource_WEBM_OPUS_pipeline_integration_fuzzer
Job Type: libfuzzer_chrome_asan
Platform Id: linux

Crash Type: CHECK failure
Crash Address: 
Crash State:
  previous_buffers_timestamp <= buffer->GetDecodeTimestamp() in webm_cluster_parse
  media::WebMClusterParser::Track::QueueBuffer
  media::WebMClusterParser::Track::AddBuffer
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_asan&range=499800:499873
Fixed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_asan&range=506278:506297

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6043553112522752

See https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reproducing.md for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz testcase 6043553112522752 is verified as fixed, so closing issue as verified.

If this is incorrect, please add ClusterFuzz-Wrong label and re-open the issue.