Even after enabling QWebEngineSettings::JavascriptCanAccessClipboard javascript document.execCommand("paste"); doesn't work.

Steps to reproduce the issue:
1. Run attached test application
2. Make sure you have some text on clipboard
3. Click on the Paste button

Expected outcome:
Text is pasted in the textfield

Actual outcome:
Text isn't pasted

Notes:
Seems that it doesn't work on Chrome(61.0.3163.100) either even though it claims paste being supported.