GitLab

According to latest editor's draft http://rawgit.com/w3c/html-api-map/master/index.html
and http://www.w3.org/WAI/PF/aria-implementation/

It should be exposed as below when header is not contained by article or section elements

MSAA+IA2
Role: IA2_ROLE_HEADER
Object attributes: xml-roles:banner

AX
AXRole: AXGroup
AXSubrole: AXLandmarkBanner
AXRoleDescription: "banner"

BUG=282262

Review URL: https://codereview.chromium.org/656293002

Cr-Commit-Position: refs/heads/master@{#300411}