[ContentEditable][IE] Wrong cursor position at the end of readonly element

[Garry Yao]

1. Load the following HTML:

<p>Para 1</p>
<p contenteditable="false">Non Editable</p>
<p>Para 2</p>

2. Put cursor at the start of the last paragraph;
3. Press Left Arrow;

Current results: Cursor is now anchored at the end of second paragraph and it's even able to type more characters.

Expected results: Cursor should skip the second paragraph and be placed at the end of the first line.

Reproduced on the ​contenteditable feature branch.