UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36
Platform: 11021.5.0 (Official Build) dev-channel kevin

Steps to reproduce the problem:
1. Go to webstore and install Sample IME for IME extension API (https://chrome.google.com/webstore/detail/sample-ime-for-ime-extens/ceaajjmckiakobniehbjpdcidfpohlin)
2. Go to tablet mode
3. Enable the input method
4. Touch any key of the input method

What is the expected behavior?
The text of the key should be entered

What went wrong?
The screen becomes black, then redraws the screen.

Did this work before? N/A 

Does this work in other browsers? Yes

Chrome version: 70.0.3538.7  Channel: dev
OS Version: 70.0.3538.7
Flash Version: 31.0.0.101

Same problem occurs with basic sample code in Chromium (https://chromium.googlesource.com/chromium/src/+/master/chrome/common/extensions/docs/examples/api/input.ime/basic/), too.