I can't reproduce this at tip-of-tree. Something looks odd on the flakiness dashboard too, because the regression range is in 2017.

The ASAN bot has a real stacktrace:
[ RUN      ] SuggestedTextTouchBarControllerUnitTest.EditingWordRangeTest
=================================================================
==18040==ERROR: AddressSanitizer: heap-use-after-free on address 0x603000211570 at pc 0x00011ca77380 bp 0x7ffee3ca5cb0 sp 0x7ffee3ca5ca8
READ of size 2 at 0x603000211570 thread T0
    #0 0x11ca7737f in icu_61::RuleBasedBreakIterator::handleNext() ??:0:0
    #1 0x11ca6fe91 in icu_61::RuleBasedBreakIterator::BreakCache::populateFollowing() ??:0:0
    #2 0x11ca6fbc8 in icu_61::RuleBasedBreakIterator::BreakCache::nextOL() ??:0:0
    #3 0x11ca7572f in icu_61::RuleBasedBreakIterator::next() ??:0:0
    #4 0x11c6ad0dc in base::i18n::BreakIterator::Advance() ??:0:0
    #5 0x124b1cbd6 in -[SuggestedTextTouchBarController editingWordRangeFromText:cursorPosition:] ??:0:0
    #6 0x111b2fef0 in SuggestedTextTouchBarControllerUnitTest_EditingWordRangeTest_Test::TestBody() ??:0:0
    #7 0x112381377 in testing::Test::Run() ??:0:0
    #8 0x112383615 in testing::TestInfo::Run() ??:0:0

https://ci.chromium.org/buildbot/chromium.memory/Mac%20ASan%2064%20Tests%20%281%29/42269

This change looks likely:
[Mac] Replace Editing Word with Selected Suggestion from Touch Bar
147c8df597ce25c86e46a7a766229732bda10e63

I just reverted this patch. Removing from the sheriff queue.

This is due to a bug in the use of ICU in the CL; reverting was the right fix. With the revert this bug is fixed.

The bug is pointed out in the review of https://chromium-review.googlesource.com/c/chromium/src/+/1130232 .