The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61

commit 4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61
Author: Biao She <bshe@chromium.org>
Date: Thu Sep 07 19:24:56 2017

Add opacity animation for viewport aware elements

Bug:  761446 
Change-Id: Id7e5db9e06c8a6ba1c9bf3108dfcb519b3d1caef
Reviewed-on: https://chromium-review.googlesource.com/648087
Commit-Queue: Biao She <bshe@chromium.org>
Reviewed-by: Ian Vollick <vollick@chromium.org>
Reviewed-by: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#500357}
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/elements/ui_element.cc
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/elements/ui_element.h
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/elements/viewport_aware_root.cc
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/elements/viewport_aware_root_unittest.cc
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/test/animation_utils.cc
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/test/animation_utils.h
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/test/ui_scene_manager_test.cc
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/test/ui_scene_manager_test.h
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/ui_input_manager_unittest.cc
[modify] https://crrev.com/4d81d6ebe5aefa4906438b1a2b5b0af3c4c71b61/chrome/browser/vr/ui_scene_unittest.cc