Build everything in events/ as part of Event target only.
Content: Add support to initialize OzoneChannel.

In Wayland case all window events need to be sent to GPU process. We have
a minimal IPC implementation, handling messages very specific to our needs.
This patch adds support to register OzoneChannel and Host as MessageFilters
after the succesfull launch of GPU and Browser process respectively.
Content: Compile content/ as part of content_common target only.

Unfortunately, the trick we could do with *.gyp files, doesn't seem to
work with *.gypi files. Thus, I had to include the files in
content_common.gypi file directly. This patch ensures that we build content
specific files only with content_common.
Remove all OzoneChannel related things from OzoneDisplay.

Now, OzoneChannelHostFactory is responsible for setting up ChannelHost
and in GPU process, we do it in GpuMain. This patch removes all related
code from OzoneDisplay.