What steps will reproduce the problem?
(1) Go to https://cdn.rawgit.com/w3c/uievents/gh-pages/tools/key-event-viewer.html
(2) Focus input field and activate MS Korean IME (assuming en-US keyboard)
(3) Press 'g' key
(4) Press Space key
(5) Observe logged events

What is the expected output?
'compositionend' should have |data='ㅎ'|.

What do you see instead?
'compositionend' have |data=''|, but an 'input' event with |data='ㅎ'| after that.

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Background:
 Issue 41945  was trying to fix this behavior (modify DOM after 'compositionend'), but it didn't work out for MS Korean IME.

Root Cause:
MS Korean IME is different from MS Japanese IME or MS Chinese IME, where (on hitting Space key during composition) Chrome will receive a WM_IME_ENDCOMPOSITION message before the WM_IME_COMPOSITION with GCS_RESULTSTR.
(The reversed order as for MS Japanese IME and MS Chinese IME)

Also see yukawa@'s comments in crrev.com/2394233002:
```
IIUC MS-IME Korean on Windows Vista and later is not directly using IMM32 APIs but using Text Services Framework (TSF) APIs instead.  Messages like WM_IME_ENDCOMPOSITION are automatically generated in the bridge layer between IMM32 and TSF called CUAS (Cicero Unaware Application Support).
```

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crrev.com/2394233002 fixed the MS Korean IME issue with a special check, but further investigations are required for the root cause.