Is this related to the servicification of the PDF component (https://crbug.com/702993) or is this to make the PPAPI version work with mus or mash?

This is about making the ppapi version work with mus ... although, it may not be a bad idea to look into servicifying pdf at the same time. Thanks for the link to that bug!

Fady says this doesn't work because BrowserPlugin doesn't support mus. Will look into what that entails.

It seems like the following needs to happen:

. RenderWidgetHostViewGuest will get a WindowTreeClient from the renderer and call ScheduleEmbed on it.
. Once RenderWidgetHostViewGuest gets the token it passes it to BrowserPlugin.
. BrowserPlugin creates a mus window using the RendererWindowTreeClient from the RenderWidget of the RenderFrameImpl of the BrowserPlugin and calls EmbedUsingToken() on it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/932e188d6de7ddff6e4c6efbac313b6c3b3f2df8

commit 932e188d6de7ddff6e4c6efbac313b6c3b3f2df8
Author: Scott Violet <sky@chromium.org>
Date: Fri Oct 20 04:29:18 2017

aura: move ScheduleEmbed to Env

I need to use this function in a place where there is no window.

BUG= 755440 
TEST=none

Change-Id: I1a547bc611236611190958fc99b63098e8b0fe19
Reviewed-on: https://chromium-review.googlesource.com/729493
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Elliot Glaysher <erg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510334}
[modify] https://crrev.com/932e188d6de7ddff6e4c6efbac313b6c3b3f2df8/content/browser/renderer_host/render_widget_host_view_aura.cc
[modify] https://crrev.com/932e188d6de7ddff6e4c6efbac313b6c3b3f2df8/ui/aura/env.cc
[modify] https://crrev.com/932e188d6de7ddff6e4c6efbac313b6c3b3f2df8/ui/aura/env.h
[modify] https://crrev.com/932e188d6de7ddff6e4c6efbac313b6c3b3f2df8/ui/aura/mus/window_port_mus.cc
[modify] https://crrev.com/932e188d6de7ddff6e4c6efbac313b6c3b3f2df8/ui/aura/mus/window_port_mus.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f1291948c56d6a1c63a7ecd72516e02431d48732

commit f1291948c56d6a1c63a7ecd72516e02431d48732
Author: Scott Violet <sky@chromium.org>
Date: Fri Oct 20 22:38:27 2017

chromeos: refactor MusEmbeddedFrame into its own file

And makes MusEmbeddedFrame talk to a delegate rather than directly to
RenderFrameProxy. BrowserPlugin is going to use this class, hence
refactoring to make it easy to adapt to both.

BUG= 755440 
TEST=none

Change-Id: Ica1fe8971e0f11b9174771b857aec5d679d8a3e6
Reviewed-on: https://chromium-review.googlesource.com/729054
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510590}
[modify] https://crrev.com/f1291948c56d6a1c63a7ecd72516e02431d48732/content/renderer/mus/BUILD.gn
[add] https://crrev.com/f1291948c56d6a1c63a7ecd72516e02431d48732/content/renderer/mus/mus_embedded_frame.cc
[add] https://crrev.com/f1291948c56d6a1c63a7ecd72516e02431d48732/content/renderer/mus/mus_embedded_frame.h
[add] https://crrev.com/f1291948c56d6a1c63a7ecd72516e02431d48732/content/renderer/mus/mus_embedded_frame_delegate.h
[modify] https://crrev.com/f1291948c56d6a1c63a7ecd72516e02431d48732/content/renderer/mus/renderer_window_tree_client.cc
[modify] https://crrev.com/f1291948c56d6a1c63a7ecd72516e02431d48732/content/renderer/mus/renderer_window_tree_client.h
[modify] https://crrev.com/f1291948c56d6a1c63a7ecd72516e02431d48732/content/renderer/render_frame_proxy.cc
[modify] https://crrev.com/f1291948c56d6a1c63a7ecd72516e02431d48732/content/renderer/render_frame_proxy.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c884c7fd53019becef8603be3e09c2cdd415fc01

commit c884c7fd53019becef8603be3e09c2cdd415fc01
Author: Scott Violet <sky@chromium.org>
Date: Fri Nov 03 23:51:01 2017

chromeos: gets WebViewGuest working with mus

With mus we want the renderer doing the embedding to create the window
on the window server and embed the guest renderer in it. This is done
by having the browser obtain the guest WindowTreeClient, call
ScheduleEmbed(), pass the token to the renderer doing the embedding
which then calls embed using the token (done using MusEmbeddedFrame).

With this flow the guest WebContents doesn't need to create an aura::Window,
that is effectively done by the renderer.

My understanding is all this code will go away within the next
quarter, so I didn't try to isolate the USE_AURA ifdefs particularly
well.

BUG= 755440 
TEST=none

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_site_isolation
Change-Id: I3efb44c02e829b46c95e595c76216c9ef61b45a4
Reviewed-on: https://chromium-review.googlesource.com/731704
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513968}
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/BUILD.gn
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/browser_main_loop.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/browser_plugin/browser_plugin_guest.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/compositor/gpu_process_transport_factory.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/frame_host/render_widget_host_view_guest.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/frame_host/render_widget_host_view_guest.h
[add] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/mus_util.cc
[add] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/mus_util.h
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/pointer_lock_browsertest.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/renderer_host/render_widget_host_unittest.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/renderer_host/render_widget_host_view_aura.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/renderer_host/render_widget_host_view_aura.h
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/renderer_host/render_widget_host_view_aura_unittest.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/renderer_host/render_widget_host_view_child_frame.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/renderer_host/render_widget_host_view_child_frame.h
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/web_contents/web_contents_impl.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/web_contents/web_contents_view_aura.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/web_contents/web_contents_view_aura.h
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/browser/web_contents/web_contents_view_guest.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/common/browser_plugin/browser_plugin_messages.h
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/renderer/browser_plugin/browser_plugin.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/renderer/browser_plugin/browser_plugin.h
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/content/renderer/mus/mus_embedded_frame.cc
[modify] https://crrev.com/c884c7fd53019becef8603be3e09c2cdd415fc01/testing/buildbot/filters/mus.browser_tests.filter

This now works. Events are not necessarily delivered correctly. That is filed here: 780279.