Predator and CL could not provide any possible suspects.
Using Code Search for the file, "cpvt_generateap.cpp" assigning to concern owner.

Suspecting Commit#
https://pdfium.googlesource.com/pdfium.git/+/67476e5ef6f122f39f547f5a14b84e9306fa136c

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

The culprit CL range is https://pdfium.googlesource.com/pdfium.git/+log/d27998f65262..d3002340caad

Ryan, it seems to be either https://pdfium-review.googlesource.com/c/10652 or https://pdfium-review.googlesource.com/c/10651

The following revision refers to this bug:
  https://pdfium.googlesource.com/pdfium/+/130bf6fc898e9ad42e3f63d90e400172de4fa65e

commit 130bf6fc898e9ad42e3f63d90e400172de4fa65e
Author: Ryan Harrison <rharrison@chromium.org>
Date: Tue Aug 15 17:25:01 2017

Add missing length check before getting element from string

BUG= chromium:754993 

Change-Id: I9444ef83fb62784fef3bf8d294b2ab88b6574b5a
Reviewed-on: https://pdfium-review.googlesource.com/11070
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

[modify] https://crrev.com/130bf6fc898e9ad42e3f63d90e400172de4fa65e/core/fpdfdoc/cpvt_generateap.cpp

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e3dedb0aef2f949e2f8236e0c38cf8fdf7c78138

commit e3dedb0aef2f949e2f8236e0c38cf8fdf7c78138
Author: pdfium-deps-roller@chromium.org <pdfium-deps-roller@chromium.org>
Date: Tue Aug 15 19:46:41 2017

Roll src/third_party/pdfium/ ae9c5cacc..130bf6fc8 (3 commits)

https://pdfium.googlesource.com/pdfium.git/+log/ae9c5cacce88..130bf6fc898e

$ git log ae9c5cacc..130bf6fc8 --date=short --no-merges --format='%ad %ae %s'
2017-08-15 rharrison Add missing length check before getting element from string
2017-08-12 thestig Do some cleanup in CPWL_Edit.
2017-08-12 thestig IFX_Edit_UndoItem implementations all take a valid CPWL_EditImpl*.

Created with:
  roll-dep src/third_party/pdfium
BUG= 754993 


Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, see:
http://www.chromium.org/developers/tree-sheriffs/sheriff-details-chromium#TOC-Failures-due-to-DEPS-rolls


TBR=dsinclair@chromium.org

Change-Id: I2890f10befe7be2d6cf242d1853752e4bc433328
Reviewed-on: https://chromium-review.googlesource.com/615661
Reviewed-by: <pdfium-deps-roller@chromium.org>
Commit-Queue: <pdfium-deps-roller@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494504}
[modify] https://crrev.com/e3dedb0aef2f949e2f8236e0c38cf8fdf7c78138/DEPS

ClusterFuzz has detected this issue as fixed in range 494482:494528.

Detailed report: https://clusterfuzz.com/testcase?key=4965557412823040

Fuzzer: ifratric_pdf_generic
Job Type: mac_asan_chrome
Platform Id: mac

Crash Type: Null-dereference READ
Crash Address: 0x000000000010
Crash State:
  GenerateWidgetAP
  FPDF_GenerateAP
  CPDF_AnnotList::CPDF_AnnotList
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=mac_asan_chrome&range=493959:493966
Fixed: https://clusterfuzz.com/revisions?job=mac_asan_chrome&range=494482:494528

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=4965557412823040

See https://github.com/google/clusterfuzz-tools 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 4965557412823040 is verified as fixed, so closing issue as verified.

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