RenderWidgetHostViewAura embeds the renderer using kEmbedFlagEmbedderInterceptsEvents. This flag means that any events normally destined for a descendant of the RWHVA go to the RWHVA. RWHVA uses kEmbedFlagEmbedderInterceptsEvents so that RWHVA can handle the event dispatch. RWHVA needs to see the real target (Window) of the event so it can dispatch properly.

With ws1 I made it so that kEmbedFlagEmbedderInterceptsEvents means the embedder sees all descendants, regardless of who created the window. This is how RWHVA ends up knowing the right target and is able to dispatch correctly. This logic was lost when transitioning to ws2 and needs to be added.

I suspect there are content_unittests/browsertests that fail with --mash now, but as we aren't running tests with this config now we aren't seeing it.

Here's the patch that added this logic to ws1: https://chromium-review.googlesource.com/c/chromium/src/+/760797 .

This functionality was only needed for content, but in talking with Sadrul and Fady it seems we may not need it. Specifically if we do 881574, then content wouldn't be using the window service for embedding renderers and this isn't an issue. I'm closing this out.
Also, here's a patch that adds this logic: https://chromium-review.googlesource.com/c/chromium/src/+/1211446 , but I'm not landing.