Earliest I could see it at:

https://build.chromium.org/p/chromium.memory.fyi/builders/Windows%20Content%20Browser%20%28DrMemory%29/builds/7297


DumpAccessibilityEventsTest.AccessibilityEventsMenuListFocus:

[160:376:0523/152604:4292851:INFO:dump_accessibility_browsertest_base.cc(202)] Testing: E:\b\build\slave\windows-content-drm-light\build\src\content\test\data\accessibility\event\menulist-focus.html (internal Blink accessibility tree)
[160:376:0523/152604:4292897:INFO:dump_accessibility_browsertest_base.cc(215)] File not found: E:\b\build\slave\windows-content-drm-light\build\src\content\test\data\accessibility\event\menulist-focus-expected-blink.txt
[160:376:0523/152604:4292897:INFO:dump_accessibility_browsertest_base.cc(216)] No expectation file present, ignoring test on this platform. To run this test anyway, create E:\b\build\slave\windows-content-drm-light\build\src\content\test\data\accessibility\event\menulist-focus-expected-blink.txt (it can be empty) and then run content_browsertests with the switch: --generate-accessibility-test-expectations
[160:376:0523/152605:4293677:INFO:dump_accessibility_browsertest_base.cc(202)] Testing: E:\b\build\slave\windows-content-drm-light\build\src\content\test\data\accessibility\event\menulist-focus.html (native accessibility tree for this platform)
c:\b\build\slave\drm-cr\build\src\content\browser\accessibility\dump_accessibility_browsertest_base.cc(356): error: Value of: is_different
Actual: true
Expected: false

Initial accessibility tree (after load complete):
9 ROLE_SYSTEM_DOCUMENT value='http://127.0.0.1:49618/accessibility/event/menulist-focus.html' READONLY FOCUSABLE tag:#document offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Times New Roman font-size:12pt font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='<obj0>' location=(0, 0) size=(800, 600) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=2 table_columns=0 row_index=0 column_index=0 n_characters=1 n_selections=0
++7 IA2_ROLE_SECTION display:block tag:body offset:0 auto-generated:false background-color:rgb(255\,255\,255) color:rgb(0\,0\,0) font-family:Arial font-size:10pt font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr role_name='body' ia2_hypertext='<obj0>' location=(8, 8) size=(784, 19) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=56637848 table_columns=56089345 row_index=56003992 column_index=56103608 n_characters=1 n_selections=0
++++6 ROLE_SYSTEM_COMBOBOX value='Apple' COLLAPSED FOCUSABLE HASPOPUP display:inline-block tag:select offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='<obj0>' default_action='open' location=(8, 8) size=(68, 19) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=57157120 table_columns=57291777 row_index=56338792 column_index=55709808 n_characters=1 n_selections=0
++++++12 ROLE_SYSTEM_LIST INVISIBLE offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='<obj0><obj1><obj2>' location=(8, 8) size=(68, 19) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=57045704 table_columns=55822337 row_index=56148272 column_index=56139584 n_characters=3 n_selections=0
++++++++13 ROLE_SYSTEM_LISTITEM name='Apple' SELECTED FOCUSABLE SELECTABLE display:block tag:option offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='Apple' default_action='click' location=(8, 8) size=(68, 19) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=55822512 table_columns=56907009 row_index=56765344 column_index=57005600 n_characters=5 n_selections=0
++++++++14 ROLE_SYSTEM_LISTITEM name='Orange' INVISIBLE FOCUSABLE SELECTABLE display:block tag:option offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='Orange' default_action='click' location=(8, 8) size=(68, 19) index_in_parent=1 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=3599617 table_columns=56925144 row_index=0 column_index=-1 n_characters=6 n_selections=0
++++++++15 ROLE_SYSTEM_LISTITEM name='Banana' INVISIBLE FOCUSABLE SELECTABLE display:block tag:option offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='Banana' default_action='click' location=(8, 8) size=(68, 19) index_in_parent=2 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=3599617 table_columns=57109072 row_index=0 column_index=-1 n_characters=6 n_selections=0


Final accessibility tree after events fired:
9 ROLE_SYSTEM_DOCUMENT value='http://127.0.0.1:49618/accessibility/event/menulist-focus.html' READONLY FOCUSABLE tag:#document offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Times New Roman font-size:12pt font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='<obj0>' location=(0, 0) size=(800, 600) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=2 table_columns=0 row_index=0 column_index=0 n_characters=1 n_selections=0
++7 IA2_ROLE_SECTION display:block tag:body offset:0 auto-generated:false background-color:rgb(255\,255\,255) color:rgb(0\,0\,0) font-family:Arial font-size:10pt font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr role_name='body' ia2_hypertext='<obj0>' location=(8, 8) size=(784, 19) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=57022976 table_columns=55805697 row_index=55902120 column_index=57056328 n_characters=1 n_selections=0
++++6 ROLE_SYSTEM_COMBOBOX value='Apple' COLLAPSED FOCUSABLE HASPOPUP display:inline-block tag:select offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-pos[160:376:0523/152612:4300931:ERROR:dump_accessibility_browsertest_base.cc(381)] Diff:
* Line Expected
- ---- --------
*    1 EVENT_OBJECT_FOCUS on role=ROLE_SYSTEM_COMBOBOX value="Apple" FOCUSED,COLLAPSED,FOCUSABLE,HASPOPUP
2 <-- End-of-file -->

Actual
------
<-- End-of-file -->
ition:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='<obj0>' default_action='open' location=(8, 8) size=(68, 19) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=55874352 table_columns=57276161 row_index=56986576 column_index=55975096 n_characters=1 n_selections=0
++++++12 ROLE_SYSTEM_LIST INVISIBLE offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='<obj0><obj1><obj2>' location=(8, 8) size=(68, 19) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=57276448 table_columns=56023809 row_index=57276384 column_index=57019256 n_characters=3 n_selections=0
++++++++13 ROLE_SYSTEM_LISTITEM name='Apple' SELECTED FOCUSABLE SELECTABLE display:block tag:option offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='Apple' default_action='click' location=(8, 8) size=(68, 19) index_in_parent=0 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=56024048 table_columns=57261569 row_index=56806432 column_index=56897704 n_characters=5 n_selections=0
++++++++14 ROLE_SYSTEM_LISTITEM name='Orange' INVISIBLE FOCUSABLE SELECTABLE display:block tag:option offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='Orange' default_action='click' location=(8, 8) size=(68, 19) index_in_parent=1 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=3599617 table_columns=56924904 row_index=0 column_index=-1 n_characters=6 n_selections=0
++++++++15 ROLE_SYSTEM_LISTITEM name='Banana' INVISIBLE FOCUSABLE SELECTABLE display:block tag:option offset:0 auto-generated:false background-color:transparent color:rgb(0\,0\,0) font-family:Arial font-weight:normal font-style:normal invalid:false language:en-US text-line-through-mode:continuous text-line-through-style:none text-line-through-text: text-line-through-type:none text-line-through-width:auto text-outline:false text-position:baseline text-shadow:none text-underline-mode:continuous text-underline-style:none text-underline-type:none text-underline-width:auto writing-mode:lr ia2_hypertext='Banana' default_action='click' location=(8, 8) size=(68, 19) index_in_parent=2 n_relations=0 group_level=0 similar_items_in_group=0 position_in_group=0 table_rows=3599617 table_columns=57281712 row_index=0 column_index=-1 n_characters=6 n_selections=0