Looking a bit more closely: it doesn't look like this information requires any privilege the mus-client cannot (or should not have). So perhaps the host does not need to send this information to the client at all? A mus-client can instead decide the mapping for itself.

If it wasn't for MacOS and the TEXTURE_RECTANGLE requirement for IOSurfaces we could easily invent a new texture target that always had to be used with images. e.g. TEXTURE_EXTERNAL_CHROMIUM. and then translate that to the correct texture target on the gpu service side depending on the type of GLImage. That would be the ideal implementation.

What if we TEXTURE_EXTERNAL_CHROMIUM and then simply say that on MacOS this target requires non-normalized texture coordinates? Then all this communication of texture just goes away. 

While that does get rid of the plumbing, do you think that makes things easier or harder to explain and understand inside compositor/media code which is dealing with textures?

I think the idea that a special texture target needs to be used with images is easy to understand as it matches OES_EGL_image_external but it might be hard to achieve as different texture target require different samplers (e.g. samplerExternalOES for EXTERNAL_OES).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d8d46ad89248600597196924ec84c29aebd7a884

commit d8d46ad89248600597196924ec84c29aebd7a884
Author: sadrul <sadrul@chromium.org>
Date: Tue Dec 20 01:21:54 2016

gpu: Move buffer format to target texture map into gpu host.

Move the code that maps <BufferFormat,BufferUsage> to GL texture
type into the gpu-host component, so that it can be used by both
chrome and mus.

BUG= 675431 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2585653003
Cr-Commit-Position: refs/heads/master@{#439651}

[modify] https://crrev.com/d8d46ad89248600597196924ec84c29aebd7a884/content/browser/compositor/gpu_process_transport_factory.cc
[modify] https://crrev.com/d8d46ad89248600597196924ec84c29aebd7a884/content/browser/gpu/browser_gpu_memory_buffer_manager.cc
[modify] https://crrev.com/d8d46ad89248600597196924ec84c29aebd7a884/content/browser/gpu/browser_gpu_memory_buffer_manager.h
[modify] https://crrev.com/d8d46ad89248600597196924ec84c29aebd7a884/content/browser/renderer_host/render_process_host_impl.cc
[modify] https://crrev.com/d8d46ad89248600597196924ec84c29aebd7a884/gpu/ipc/host/gpu_memory_buffer_support.cc
[modify] https://crrev.com/d8d46ad89248600597196924ec84c29aebd7a884/gpu/ipc/host/gpu_memory_buffer_support.h
[modify] https://crrev.com/d8d46ad89248600597196924ec84c29aebd7a884/ui/aura/mus/mus_context_factory.cc
[modify] https://crrev.com/d8d46ad89248600597196924ec84c29aebd7a884/ui/compositor/compositor.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7ac76b9328da7ec9531dab33484242fc3e3f980d

commit 7ac76b9328da7ec9531dab33484242fc3e3f980d
Author: sadrul <sadrul@chromium.org>
Date: Tue Dec 20 01:55:20 2016

gpu: Simplify the mapping from BufferFormat to texture type.

The texture type is always GL_TEXTURE_2D on non-ozone non-macos platforms.
Make that more obvious when reading the code.

BUG= 675431 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2587823002
Cr-Commit-Position: refs/heads/master@{#439664}

[modify] https://crrev.com/7ac76b9328da7ec9531dab33484242fc3e3f980d/gpu/ipc/host/gpu_memory_buffer_support.cc

If mus uses ozone, mus can ask it to ClientNativePixmapFactory, which is singleton in renderer and non-privileged process.
To query it correctly in renderer, renderer needs to know if native GBM is enabled.
https://codereview.chromium.org/2649553003/ lets renderer know  if native GBM is enabled.

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available. If you change it back, also remove the "Hotlist-Recharge-Cold" label.

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

vmiura's https://chromium-review.googlesource.com/849491 makes this sane, in that it is passed to the client as part of the gpu::Capabilities, and so the client can call gpu::GetBufferTextureTarget and get the right mapping. I'm going to call this fixed.