Predator did not provide any possible suspects.
Assigning to the concern owner from CL --
https://chromium.googlesource.com/chromium/src/+log/784971913adcc32bdb22a92da6ac237a7de88a2b..ff280f67ab2bca6f1935e6d0061d9145a24a9526?pretty=fuller

Suspecting CL --
https://chromium.googlesource.com/chromium/src/+/b9dc835015e914ded4f4f3db0bd9e95aaf7d7c03

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

https://pdfium-review.googlesource.com/c/5090/

The following revision refers to this bug:
  https://pdfium.googlesource.com/pdfium/+/486f141ed1fa5b92f59d403c4b549ede2ea1a2c8

commit 486f141ed1fa5b92f59d403c4b549ede2ea1a2c8
Author: Dan Sinclair <dsinclair@chromium.org>
Date: Mon May 08 18:38:02 2017

Check bits to decode will fit before decoding

When decoding the CPDF_HintTable we read the dwDeltaGroupLen value out
of the input stream which is a 16bit number. That value is then passed
in to read a uint32_t of the object number. If we have a group length of
> 32 bits we'll cause an undefined shift when we attempt to shift right
more then 32 bits.

This Cl bails out early if the dwDeltaGroupLen value is > 32 in order to
stop the undefined shifts.

Bug:  chromium:718505 
Change-Id: I919d6f4cd19826094a5e44d3a65d758029f5c236
Reviewed-on: https://pdfium-review.googlesource.com/5090
Reviewed-by: dsinclair <dsinclair@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>

[modify] https://crrev.com/486f141ed1fa5b92f59d403c4b549ede2ea1a2c8/core/fpdfapi/parser/cpdf_hint_tables.cpp

ClusterFuzz has detected this issue as fixed in range 470053:470151.

Detailed report: https://clusterfuzz.com/testcase?key=6128384259391488

Fuzzer: libfuzzer_pdf_hint_table_fuzzer
Job Type: libfuzzer_chrome_ubsan
Platform Id: linux

Crash Type: Undefined-shift
Crash Address: 
Crash State:
  CFX_BitStream::GetBits
  CPDF_HintTables::ReadSharedObjHintTable
  HintTableForFuzzing::Fuzz
  
Sanitizer: undefined (UBSAN)

Regressed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=413192:413325
Fixed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=470053:470151

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6128384259391488


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.