UserAgent: Mozilla/5.0 (X11; Linux i686) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/53.0.2785.143 Chrome/53.0.2785.143 Safari/537.36

Steps to reproduce the problem:
1. Create a form with a field : <input type="text" id="register_username" name="username" required="required" maxlength="255" pattern="[a-z\']*" placeholder="Nom d'utilisateur" class="main-input not-removable"> 
2. Load the page
3. Type abc in form
4. Validate the form

What is the expected behavior?
It should validate the form but it says that text is invalid.

What went wrong?
Says the text is invalid.

pattern="[a-z]*" works great
pattern="[a-z\']*" doesn't work

Did this work before? Yes 

Chrome version: 53.0.2785.143  Channel: stable
OS Version: Ubuntu 16.04 LTS
Flash Version: