It's just failing because RWHVChildFrame::CopyFromSurface earlies out for reasons that are no longer valid. The fix is easy and I already have a CL sent out.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8ac4b5e605f2b3920f38ebbd0c6b9735cbb83e50

commit 8ac4b5e605f2b3920f38ebbd0c6b9735cbb83e50
Author: Saman Sami <samans@chromium.org>
Date: Thu Nov 08 23:02:16 2018

Fix RHWVChildFrame::CopyFromSurface

Currently this method earlies out and returns an empty SkBitmap if
OOP-D is enabled. It should just proceed the same way as the
non-OOP-D case.

Bug:  903453 
Change-Id: I0943279e2d98885682f5b8d4e619413293575b5a
Reviewed-on: https://chromium-review.googlesource.com/c/1327418
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Commit-Queue: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606637}
[modify] https://crrev.com/8ac4b5e605f2b3920f38ebbd0c6b9735cbb83e50/content/browser/renderer_host/render_widget_host_view_child_frame.cc

We need to merge this back to M71. We are planning to ship VizDisplayCompositor in M71 and right now webview.captureVisibleRegion does not work when viz is enabled. The CL is very safe, it just removes a portion of code that we forgot to delete when  https://crbug.com/812059  was fixed.

This bug requires manual review: Less than 21 days to go before AppStore submit on M71
Please contact the milestone owner if you have questions.
Owners: benmason@(Android), kariahda@(iOS), kbleicher@(ChromeOS), govind@(Desktop)

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

Approving merge to M71 branch 3578 based on comment #1. Please merge ASAP. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/39243aecde5bd420b0982d8ab1abc8731b8c3b9c

commit 39243aecde5bd420b0982d8ab1abc8731b8c3b9c
Author: Saman Sami <samans@chromium.org>
Date: Fri Nov 09 16:14:02 2018

Fix RHWVChildFrame::CopyFromSurface

Currently this method earlies out and returns an empty SkBitmap if
OOP-D is enabled. It should just proceed the same way as the
non-OOP-D case.

Bug:  903453 
Change-Id: I0943279e2d98885682f5b8d4e619413293575b5a
Reviewed-on: https://chromium-review.googlesource.com/c/1327418
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Commit-Queue: Saman Sami <samans@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#606637}(cherry picked from commit 8ac4b5e605f2b3920f38ebbd0c6b9735cbb83e50)
Reviewed-on: https://chromium-review.googlesource.com/c/1329445
Reviewed-by: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/branch-heads/3578@{#612}
Cr-Branched-From: 4226ddf99103e493d7afb23a4c7902ee496108b6-refs/heads/master@{#599034}
[modify] https://crrev.com/39243aecde5bd420b0982d8ab1abc8731b8c3b9c/content/browser/renderer_host/render_widget_host_view_child_frame.cc

The following revision refers to this bug: 
https://chromium.googlesource.com/chromium/src.git/+/39243aecde5bd420b0982d8ab1abc8731b8c3b9c

Commit: 39243aecde5bd420b0982d8ab1abc8731b8c3b9c
Author: samans@chromium.org
Commiter: samans@chromium.org
Date: 2018-11-09 16:14:02 +0000 UTC

Fix RHWVChildFrame::CopyFromSurface

Currently this method earlies out and returns an empty SkBitmap if
OOP-D is enabled. It should just proceed the same way as the
non-OOP-D case.

Bug:  903453 
Change-Id: I0943279e2d98885682f5b8d4e619413293575b5a
Reviewed-on: https://chromium-review.googlesource.com/c/1327418
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Commit-Queue: Saman Sami <samans@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#606637}(cherry picked from commit 8ac4b5e605f2b3920f38ebbd0c6b9735cbb83e50)
Reviewed-on: https://chromium-review.googlesource.com/c/1329445
Reviewed-by: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/branch-heads/3578@{#612}
Cr-Branched-From: 4226ddf99103e493d7afb23a4c7902ee496108b6-refs/heads/master@{#599034}