The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/69853f24e2e78479ee4407086333b4a2e9e86e04

commit 69853f24e2e78479ee4407086333b4a2e9e86e04
Author: Brandon Jones <bajones@chromium.org>
Date: Thu Jun 21 00:45:32 2018

Added XREnvironmentBlendMode

Adds environmenBlendMode attribute to XRSession. Currently relies on the
XR Hit Test flag to determine if the mode is something is other than
"opaque" because that's the only signal we have for now. Should
ultimately communicate this from the browser side so that devices can
report their optical properties on a case-by-case basis.

Bug:  854284 
Change-Id: I13f3f41d104e017b087a32b32f3d00686513f9f1
Reviewed-on: https://chromium-review.googlesource.com/1109261
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Commit-Queue: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569103}
[modify] https://crrev.com/69853f24e2e78479ee4407086333b4a2e9e86e04/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[add] https://crrev.com/69853f24e2e78479ee4407086333b4a2e9e86e04/third_party/WebKit/LayoutTests/xr/xrSession_environmentBlendMode.html
[modify] https://crrev.com/69853f24e2e78479ee4407086333b4a2e9e86e04/third_party/blink/renderer/modules/xr/xr_device.cc
[modify] https://crrev.com/69853f24e2e78479ee4407086333b4a2e9e86e04/third_party/blink/renderer/modules/xr/xr_session.cc
[modify] https://crrev.com/69853f24e2e78479ee4407086333b4a2e9e86e04/third_party/blink/renderer/modules/xr/xr_session.h
[modify] https://crrev.com/69853f24e2e78479ee4407086333b4a2e9e86e04/third_party/blink/renderer/modules/xr/xr_session.idl