Which CL caused this? Based on the M-63 label, I assume it was one before the branch cut and we need to merge.

Can we write an automated test for this? Run some JS in the VR browser that checks for the pose and ensures it is null?

Yes, adding tests is easy and it was an oversight we didn't before.

https://chromium-review.googlesource.com/c/chromium/src/+/709956 broke this, the fix is in https://chromium-review.googlesource.com/c/chromium/src/+/723770

We do need to merge.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/417f0e75b6ea9652ccc64e8951a47cc2c79104e1

commit 417f0e75b6ea9652ccc64e8951a47cc2c79104e1
Author: Michael Thiessen <mthiesse@chromium.org>
Date: Tue Oct 17 23:51:17 2017

VR: Prevent WebVR from receiving poses while in VR browsing mode.

This CL is kept intentionally as simple as possible for merging back to
M-63.

Tests to prevent this regression in the future will be added in a
followup CL.

Bug:  775571 
Change-Id: I78ea1e46efdb2b48bc61e1ab704b6b1526d2c171
Reviewed-on: https://chromium-review.googlesource.com/723770
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509606}
[modify] https://crrev.com/417f0e75b6ea9652ccc64e8951a47cc2c79104e1/chrome/browser/android/vr_shell/vr_shell_delegate.cc
[modify] https://crrev.com/417f0e75b6ea9652ccc64e8951a47cc2c79104e1/device/vr/android/gvr/gvr_device.cc
[modify] https://crrev.com/417f0e75b6ea9652ccc64e8951a47cc2c79104e1/device/vr/android/gvr/gvr_device.h

Your change meets the bar and is auto-approved for M63. Please go ahead and merge the CL to branch 3239 manually. Please contact milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), gkihumba@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Filed  issue 777868  to track adding a regression test.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5aa44f5dbddbdf86f2ae8ec04f6b70bde080ab1f

commit 5aa44f5dbddbdf86f2ae8ec04f6b70bde080ab1f
Author: Michael Thiessen <mthiesse@chromium.org>
Date: Tue Oct 24 14:50:24 2017

VR: Prevent WebVR from receiving poses while in VR browsing mode.

This CL is kept intentionally as simple as possible for merging back to
M-63.

Tests to prevent this regression in the future will be added in a
followup CL.

TBR=mthiesse@chromium.org

(cherry picked from commit 417f0e75b6ea9652ccc64e8951a47cc2c79104e1)

Bug:  775571 
Change-Id: I78ea1e46efdb2b48bc61e1ab704b6b1526d2c171
Reviewed-on: https://chromium-review.googlesource.com/723770
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Michael Thiessen <mthiesse@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#509606}
Reviewed-on: https://chromium-review.googlesource.com/735741
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/branch-heads/3239@{#175}
Cr-Branched-From: adb61db19020ed8ecee5e91b1a0ea4c924ae2988-refs/heads/master@{#508578}
[modify] https://crrev.com/5aa44f5dbddbdf86f2ae8ec04f6b70bde080ab1f/chrome/browser/android/vr_shell/vr_shell_delegate.cc
[modify] https://crrev.com/5aa44f5dbddbdf86f2ae8ec04f6b70bde080ab1f/device/vr/android/gvr/gvr_device.cc
[modify] https://crrev.com/5aa44f5dbddbdf86f2ae8ec04f6b70bde080ab1f/device/vr/android/gvr/gvr_device.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b856d8615328453536f0fd12972e07b3552d48bd

commit b856d8615328453536f0fd12972e07b3552d48bd
Author: Michael Thiessen <mthiesse@chromium.org>
Date: Tue Oct 24 18:47:54 2017

Revert "VR: Prevent WebVR from receiving poses while in VR browsing mode."

This reverts commit 5aa44f5dbddbdf86f2ae8ec04f6b70bde080ab1f.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> VR: Prevent WebVR from receiving poses while in VR browsing mode.
> 
> This CL is kept intentionally as simple as possible for merging back to
> M-63.
> 
> Tests to prevent this regression in the future will be added in a
> followup CL.
> 
> TBR=mthiesse@chromium.org
> 
> (cherry picked from commit 417f0e75b6ea9652ccc64e8951a47cc2c79104e1)
> 
> Bug:  775571 
> Change-Id: I78ea1e46efdb2b48bc61e1ab704b6b1526d2c171
> Reviewed-on: https://chromium-review.googlesource.com/723770
> Reviewed-by: Brandon Jones <bajones@chromium.org>
> Commit-Queue: Michael Thiessen <mthiesse@chromium.org>
> Cr-Original-Commit-Position: refs/heads/master@{#509606}
> Reviewed-on: https://chromium-review.googlesource.com/735741
> Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
> Cr-Commit-Position: refs/branch-heads/3239@{#175}
> Cr-Branched-From: adb61db19020ed8ecee5e91b1a0ea4c924ae2988-refs/heads/master@{#508578}

TBR=mthiesse@chromium.org,bajones@chromium.org

Change-Id: I9447befdc77fea63f438bae24ce99f91785c442d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  775571 
Reviewed-on: https://chromium-review.googlesource.com/735460
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/branch-heads/3239@{#184}
Cr-Branched-From: adb61db19020ed8ecee5e91b1a0ea4c924ae2988-refs/heads/master@{#508578}
[modify] https://crrev.com/b856d8615328453536f0fd12972e07b3552d48bd/chrome/browser/android/vr_shell/vr_shell_delegate.cc
[modify] https://crrev.com/b856d8615328453536f0fd12972e07b3552d48bd/device/vr/android/gvr/gvr_device.cc
[modify] https://crrev.com/b856d8615328453536f0fd12972e07b3552d48bd/device/vr/android/gvr/gvr_device.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b21684e0db86e75b3dc6e8219c391df00805b0f3

commit b21684e0db86e75b3dc6e8219c391df00805b0f3
Author: Michael Thiessen <mthiesse@chromium.org>
Date: Wed Oct 25 17:33:41 2017

Reland "VR: Prevent WebVR from receiving poses while in VR browsing mode."

This reverts commit b856d8615328453536f0fd12972e07b3552d48bd.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Revert "VR: Prevent WebVR from receiving poses while in VR browsing mode."
> 
> This reverts commit 5aa44f5dbddbdf86f2ae8ec04f6b70bde080ab1f.
> 
> Reason for revert: <INSERT REASONING HERE>
> 
> Original change's description:
> > VR: Prevent WebVR from receiving poses while in VR browsing mode.
> > 
> > This CL is kept intentionally as simple as possible for merging back to
> > M-63.
> > 
> > Tests to prevent this regression in the future will be added in a
> > followup CL.
> > 
> > TBR=mthiesse@chromium.org
> > 
> > (cherry picked from commit 417f0e75b6ea9652ccc64e8951a47cc2c79104e1)
> > 
> > Bug:  775571 
> > Change-Id: I78ea1e46efdb2b48bc61e1ab704b6b1526d2c171
> > Reviewed-on: https://chromium-review.googlesource.com/723770
> > Reviewed-by: Brandon Jones <bajones@chromium.org>
> > Commit-Queue: Michael Thiessen <mthiesse@chromium.org>
> > Cr-Original-Commit-Position: refs/heads/master@{#509606}
> > Reviewed-on: https://chromium-review.googlesource.com/735741
> > Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
> > Cr-Commit-Position: refs/branch-heads/3239@{#175}
> > Cr-Branched-From: adb61db19020ed8ecee5e91b1a0ea4c924ae2988-refs/heads/master@{#508578}
> 
> TBR=mthiesse@chromium.org,bajones@chromium.org
> 
> Change-Id: I9447befdc77fea63f438bae24ce99f91785c442d
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug:  775571 
> Reviewed-on: https://chromium-review.googlesource.com/735460
> Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
> Cr-Commit-Position: refs/branch-heads/3239@{#184}
> Cr-Branched-From: adb61db19020ed8ecee5e91b1a0ea4c924ae2988-refs/heads/master@{#508578}

TBR=mthiesse@chromium.org,bajones@chromium.org

Change-Id: I0527e0ca6fe7a0051f0244bd66c86e1ed59f864c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  775571 
Reviewed-on: https://chromium-review.googlesource.com/737864
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/branch-heads/3239@{#223}
Cr-Branched-From: adb61db19020ed8ecee5e91b1a0ea4c924ae2988-refs/heads/master@{#508578}
[modify] https://crrev.com/b21684e0db86e75b3dc6e8219c391df00805b0f3/chrome/browser/android/vr_shell/vr_shell_delegate.cc
[modify] https://crrev.com/b21684e0db86e75b3dc6e8219c391df00805b0f3/device/vr/android/gvr/gvr_device.cc
[modify] https://crrev.com/b21684e0db86e75b3dc6e8219c391df00805b0f3/device/vr/android/gvr/gvr_device.h