Not sure yet if these have the same root cause, but on

https://luci-milo.appspot.com/buildbot/chromium.android/Marshmallow%2064%20bit%20Tester/

all of the following org.chromium.chrome.browser.* tests seem to have started flaking at about the same time:

appmenu.ChromeHomeAppMenuTest#testPageMenu                                     -FFFFFFFF-FF-F-F---------
appmenu.ChromeHomeAppMenuTest#testTabSwitcherMenu                              FFFFFFFFFFF--F-----------
ntp.ChromeHomeNewTabPageTest#testCloseNTP_Incognito                            F------FF-FF--FF---------
ntp.ChromeHomeNewTabPageTest#testCloseNTP_OneTab                               F-F-FF-FFFF----F---------
ntp.ChromeHomeNewTabPageTest#testCloseNTP_TwoTabs                              --F-FF--FFFF---F---------
ntp.ChromeHomeNewTabPageTest#testCloseNTP_TwoTabs_OverviewMode                 FF---FFF-FFF-F-----------
ntp.ChromeHomeNewTabPageTest#testToggleSelectedTab                             F--FFF--FFF--F-----------
suggestions.SuggestionsBottomSheetTest#testContextMenu                         F-F----F-----F-----------
widget.bottomsheet.BottomSheetObserverTest#testCloseEventCalledNoAnimation     F-F--FFFFFF--FF----------
widget.bottomsheet.BottomSheetObserverTest#testCloseEventCalledWithAnimation   FFFF-FFFFF-F-F-F---------
widget.bottomsheet.BottomSheetObserverTest#testOffsetChangedEvent              F-FF-FFFFF-F---F---------
widget.bottomsheet.BottomSheetObserverTest#testOpenedEventCalledNoAnimation    FFF-F--F-FF--FF----------
widget.bottomsheet.BottomSheetObserverTest#testOpenedEventCalledWithAnimation  ---FFFFFFFFF-F-F---------
widget.bottomsheet.BottomSheetObserverTest#testPeekToHalfTransition            -F-FFFFFFF-F-FFF---------
widget.bottomsheet.BottomSheetObserverTest#testSheetContentChanged             FFF-FFFFFFFF-FFF---------

The first failures appeared during:
https://luci-milo.appspot.com/buildbot/chromium.android/Marshmallow%2064%20bit%20Tester/11523

With the following CL range:
http://test-results.appspot.com/revision_range?start=466772&end=466800

From that range the following CL stands out:
"[Home] Polish bottom sheet content transitions"
https://codereview.chromium.org/2839673002

mdjones@ could you investigate?