Change record status: 
Project: 
Introduced in branch: 
8.x
Description: 

We now send the X-UA-Compatible HTTP header to force IE to use the most recent rendering engine or use Chrome's frame rendering engine if available.

This also prevents the IE compatibility mode button to appear if certain markup makes IE think it is dealing with legacy pages (such as when using IE conditional classes on the html tag.)

This is the HTTP header that now appears in Drupal 8:

X-UA-Compatible: IE=edge,chrome=1
Impacts: 
Site builders, administrators, editors
Themers
Updates Done (doc team, etc.)
Online documentation: 
Not done
Theming guide: 
Not done
Module developer documentation: 
Not done
Examples project: 
Not done
Coder Review: 
Not done
Coder Upgrade: 
Not done
Other: 
Other updates done