Predator and CL did not find any possible suspects.
Using Code Search for the file, "launcher_context_menu.cc" assigning to the concern owner.
Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/f7d4caad1b47aa9b28713a164a1435feb31946c7

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

I don't see how SessionManager::Get could be nullptr for chromeos. I suspect the crash is actually because of null |controller_| (aka ChromeLauncherControllerImpl, or ShelfDelegate). ShelfDelegate is now created with session state chage via mojo asynchronously. And there are possibilities that mouse events is handled before the mojo message is processed. In such case, we crash around line 190 in LauncherContextMenu::AddShelfOptionsMenu when trying to use controller_->profile().

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/70adf8ced0a1e191f0dabdec73b568c26f1ca2d2

commit 70adf8ced0a1e191f0dabdec73b568c26f1ca2d2
Author: xiyuan <xiyuan@chromium.org>
Date: Fri Feb 10 21:40:29 2017

ash: Fix clusterfuzz crash in AddShelfOptionsMenu

Ash ShelfDelegate is created on session state change to ACTIVE
via mojo asynchronously. Mouse events could happen during that
time to trigger shelf context menu and crash. Replace DCHECK
with an "if" to handle such case since it is possible now.

BUG= 690902 
TEST=clusterfuzz

Review-Url: https://codereview.chromium.org/2693513002
Cr-Commit-Position: refs/heads/master@{#449743}

[modify] https://crrev.com/70adf8ced0a1e191f0dabdec73b568c26f1ca2d2/chrome/browser/ui/ash/chrome_shell_delegate.cc

ClusterFuzz has detected this issue as fixed in range 449725:449806.

Detailed report: https://cluster-fuzz.appspot.com/testcase?key=6514338065285120

Fuzzer: meacer_chromebot_extensions
Job Type: linux_asan_chrome_chromeos
Platform Id: linux

Crash Type: UNKNOWN READ
Crash Address: 0x000000000010
Crash State:
  LauncherContextMenu::AddShelfOptionsMenu
  LauncherContextMenu::Create
  ChromeShellDelegate::CreateContextMenu
  
Sanitizer: address (ASAN)

Regressed: https://cluster-fuzz.appspot.com/revisions?job=linux_asan_chrome_chromeos&range=444406:444508
Fixed: https://cluster-fuzz.appspot.com/revisions?job=linux_asan_chrome_chromeos&range=449725:449806

Reproducer Testcase: https://cluster-fuzz.appspot.com/download/AMIfv941NLsYy76zCwshegk01V7NImRFZoTjmPzS5eQ6ixl8vPWkHDNBrEfp2Rfqkaqe5JQst8SQygWmOdOIHxoLMtfNNHCy1STXmxfMr1KnimRU8SiOrEmN2ead54yEZghC3i1nzjHaWw-F-jVAZsNiu2duK9iu94ywtT95pRCyfJAPkHnwLHGayI_dkC3RzzujVrXVsQXluNMbKgMr7urUB9mizjPEUnPiHvXeJl3NrmrxXyTqDs4gkrkJS7uMyDvgch6Uzc8ZetutuiL1ebJULeyWC9bXdzn6m1N6hEqEnPQZaol28mN_6Ox4nsiFo4H7TDZ7A_AyC20joMo2rE8GR4ckNIPxDJcnfVX2dq_9KbTjiPmUyggR0WpoFsuCEozY2w7SDJN5MCnCdbm5gB_RWsi0qIOpLw?testcase_id=6514338065285120


Additional requirements: Requires Gestures

See https://dev.chromium.org/Home/chromium-security/bugs/reproducing-clusterfuzz-bugs for more information.

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