On my emulator it simply crashed when I began handwriting - that was when the custom cursor should be displayed.

Debugging information:

Program received signal SIGSEGV, Segmentation fault.
ui::X11WindowOzone::SetCursor (this=0x23dcbdfca180, cursor=0x0) at ../../ui/platform_window/x11/x11_window_ozone.cc:49
49	  XDefineCursor(xdisplay(), xwindow(), cursor_ozone->xcursor());
(gdb) bt
#0  ui::X11WindowOzone::SetCursor (this=0x23dcbdfca180, cursor=0x0) at ../../ui/platform_window/x11/x11_window_ozone.cc:49
#1  0x000055555940c060 in aura::WindowTreeHost::SetCursor (this=0x23dcbe5273c8, cursor=...) at ../../ui/aura/window_tree_host.cc:164
#2  0x0000555559fc0c61 in ash::(anonymous namespace)::SetCursorOnAllRootWindows (cursor=...) at ../../ash/wm/native_cursor_manager_ash_classic.cc:25
#3  0x0000555559fc0bf2 in ash::NativeCursorManagerAshClassic::SetCursor (this=<optimized out>, cursor=..., delegate=0x23dcbde81108) at ../../ash/wm/native_cursor_manager_ash_classic.cc:119
#4  0x000055555b51bfe4 in wm::CursorManager::SetCursor (this=<optimized out>, cursor=...) at ../../ui/wm/core/cursor_manager.cc:98
#5  0x0000555556d42f70 in content::RenderWidgetHostViewAura::UpdateCursorIfOverSelf (this=<optimized out>) at ../../content/browser/renderer_host/render_widget_host_view_aura.cc:2069
#6  0x0000555556d42e44 in content::RenderWidgetHostViewAura::DisplayCursor (this=0x23dcc1f87e00, cursor=...) at ../../content/browser/renderer_host/render_widget_host_view_aura.cc:828
#7  0x0000555556ccb8a7 in content::CursorManager::UpdateCursor (this=0x23dcbe9daba0, view=<optimized out>, cursor=...) at ../../content/browser/renderer_host/cursor_manager.cc:20
#8  0x0000555556d3520e in DispatchToMethodImpl<content::RenderWidgetHostImpl*, void (content::RenderWidgetHostImpl::*)(content::WebCursor const&), std::__1::tuple<content::WebCursor>, 0> (method=<optimized out>, 
    args=<unknown type in /usr/local/google/home/chengong/chrome/src/out/myos/chrome, CU 0xbe2b071, DIE 0xbea2f4c>, obj=<optimized out>) at ../../base/tuple.h:52
#9  DispatchToMethod<content::RenderWidgetHostImpl*, void (content::RenderWidgetHostImpl::*)(content::WebCursor const&), std::__1::tuple<content::WebCursor> > (obj=<optimized out>, method=<optimized out>, args=<optimized out>)
    at ../../base/tuple.h:60
#10 DispatchToMethod<content::RenderWidgetHostImpl, void (content::RenderWidgetHostImpl::*)(content::WebCursor const&), void, std::__1::tuple<content::WebCursor> > (obj=<optimized out>, method=<optimized out>, 
    tuple=<optimized out>) at ../../ipc/ipc_message_templates.h:51
#11 IPC::MessageT<ViewHostMsg_SetCursor_Meta, std::__1::tuple<content::WebCursor>, void>::Dispatch<content::RenderWidgetHostImpl, content::RenderWidgetHostImpl, void, void (content::RenderWidgetHostImpl::*)(content::WebCursor const&)> (msg=0x23dcbe907038, obj=<optimized out>, sender=<optimized out>, parameter=<optimized out>, func=<optimized out>) at ../../ipc/ipc_message_templates.h:146
#12 0x0000555556d33b45 in content::RenderWidgetHostImpl::OnMessageReceived (this=0x23dcbfadce00, msg=...) at ../../content/browser/renderer_host/render_widget_host_impl.cc:613
#13 0x000055555833e2cb in IPC::ChannelProxy::Context::OnDispatchMessage (this=0x23dcbe9643c0, message=...) at ../../ipc/ipc_channel_proxy.cc:320
#14 0x00005555580fdcff in Run (this=<optimized out>) at ../../base/callback.h:65
#15 base::debug::TaskAnnotator::RunTask (this=<optimized out>, queue_function=<optimized out>, pending_task=0x7fffffffceb0) at ../../base/debug/task_annotator.cc:55
#16 0x0000555558114677 in base::MessageLoop::RunTask (this=0x23dcbdcf5c80, pending_task=0x7fffffffceb0) at ../../base/message_loop/message_loop.cc:391
#17 0x0000555558114b59 in DeferOrRunPendingTask (this=<optimized out>, pending_task=...) at ../../base/message_loop/message_loop.cc:403
#18 base::MessageLoop::DoWork (this=0x23dcbdcf5c80) at ../../base/message_loop/message_loop.cc:447
#19 0x0000555558115cc9 in base::MessagePumpLibevent::Run (this=0x23dcbdd80600, delegate=0x23dcbdcf5c80) at ../../base/message_loop/message_pump_libevent.cc:220
#20 0x00005555581326a4 in base::RunLoop::Run (this=0x7fffffffd020) at ../../base/run_loop.cc:114
#21 0x0000555557e4c3fb in ChromeBrowserMainParts::MainMessageLoopRun (this=0x23dcbdcf4b00, result_code=<optimized out>) at ../../chrome/browser/chrome_browser_main.cc:1934
#22 0x0000555556aba3a7 in content::BrowserMainLoop::RunMainMessageLoopParts (this=0x23dcbdd10a80) at ../../content/browser/browser_main_loop.cc:1196
#23 0x0000555556abcd92 in content::BrowserMainRunnerImpl::Run (this=0x23dcbdd24140) at ../../content/browser/browser_main_runner.cc:140
#24 0x0000555556ab66dc in content::BrowserMain (parameters=...) at ../../content/browser/browser_main.cc:46
#25 0x0000555557e3a985 in content::ContentMainRunnerImpl::Run (this=0x23dcbdcf2f00) at ../../content/app/content_main_runner.cc:705
#26 0x0000555557e426fc in service_manager::Main (params=...) at ../../services/service_manager/embedder/main.cc:456
#27 0x0000555557e395e4 in content::ContentMain (params=...) at ../../content/app/content_main.cc:19
#28 0x0000555556382387 in ChromeMain (argc=<optimized out>, argv=<optimized out>) at ../../chrome/app/chrome_main.cc:130
#29 0x00007ffff47b42b1 in __libc_start_main () from /lib/x86_64-linux-gnu/libc.so.6
#30 0x0000555556381f2a in _start ()
(gdb) print cursor_ozone
$1 = (ui::X11CursorOzone *) 0x0
(gdb) print cursor
$2 = (ui::PlatformCursor) 0x0
(gdb)  

I change status to 'Assigned' because it already has an owner.

This bug has a target milestone that has passed.  Please help bug cleanup: mark it closed or update/remove the milestone target. 

Regressions should be P1 as a general rule.  Chengong can you advise?

doesn't repro in M71 (switched back to old ui via chrome://flags)