ReadOnly editor does not fire focus events

[Dusty Jewett]

Steps to reproduce

1. Add focus listener to editor
2. set editor to read only
3. click on editor

See: ​https://jsbin.com/fevaxa/edit?html,js,output

Expected result

Editor should fire focus events

Actual result

Editor does not fire focus events.

Other details (browser, OS, CKEditor version, installed plugins)

This bug is caused by the implementation of setReadOnly, which, contrary to it's name, does not set 'readonly', but rather sets contenteditable=false, which is NOT the same.

Input-related events no longer fire, and the component behaves differently because of this.

It appears that this has been the case since 2012, with no changes or modifications in the mean time.

[Dusty Jewett]

Pull Request Submitted: ​https://github.com/ckeditor/ckeditor-dev/pull/220

[kkrzton]

Confirmed for CKEditor 4.5.8 on Chrome 49.