media: Plumb MediaLog to MojoVideoDecoderService.

media/mojo/clients/BUILD.gn

Index: media/mojo/clients/BUILD.gn
diff --git a/media/mojo/clients/BUILD.gn b/media/mojo/clients/BUILD.gn
index a299b51d0e63a3fd38d39ff878900e19a166b9a3..6b860939236addaa6cb0f050fca95ebb5b11b54f 100644
--- a/media/mojo/clients/BUILD.gn
+++ b/media/mojo/clients/BUILD.gn
@@ -11,7 +11,6 @@ source_set("clients") {
     # TODO(xhwang): Only allow //media/mojo:media_mojo_unittests
     "//media/mojo:*",
 
-    # TODO(xhwang): Only allow //media/mojo/services:media_service_unittests
     "//media/mojo/services:*",
 
     "//media/test/*",
@@ -35,6 +34,8 @@ source_set("clients") {
     "mojo_decryptor.h",
     "mojo_demuxer_stream_impl.cc",
     "mojo_demuxer_stream_impl.h",
+    "mojo_media_log.cc",
+    "mojo_media_log.h",

[xhwang, 2017/06/30 16:24:57]

This is actually used on the "service" side...

[sandersd (OOO until July 31), 2017/06/30 17:44:30]

This is a client in the same sense as MojoVideoDecoder--it uses a Mojo service
to implement media::MediaLog for clients. The service side consumes a
media::MediaLog and provides a Mojo interface to it.

[xhwang, 2017/06/30 19:54:24]

I see your point and I admit it's a bit confusing. Here're some randoms
thoughts:

1. The name "clients" and "services" are too generic. We should probably rename
"services" to "playback_services". (See Dale's doc on "playback" at [1]). It
should not be a placeholder for all mojo interface implementations.

2. Historically, "services" means everything running in the MediaService in the
remote process.

3. And "clients" means the client side running in the render process. That's why
"clients" have the visibility on "//content/renderer:*" (lien 9)*.
"mojo_demuxer_stream_impl.h" is an example that it implements a mojo interface
to be used by objects in the MediaService. Similarly, we should probably put
"mojo_media_log_service.*" here, not "mojo_media_log.*".

4. We could adopt your model and put all "mojom implementations" in "services",
ignoring which group of classes actually work together. This is how our "media"
target works. But I feel the gist of GN is that you can have many smaller
targets which are logically self-contained, but I could be wrong or at least too
aggressive on that.

[1]
https://cs.chromium.org/chromium/src/media/README.md?rcl=12dd20d1972b5a0a2100...

*  Nothing prevents us to run such a client in another process (e.g. utility),
but since "clients" is a source_set, that could cause duplicated static symbols
which could lead to bugs in component builds.

[sandersd (OOO until July 31), 2017/07/06 21:25:24]

I'm having trouble turning this into a plan forward for this CL. How would you
like me to group these particular classes for now?

[sandersd (OOO until July 31), 2017/07/07 21:48:47]

Done.

     "mojo_renderer.cc",
     "mojo_renderer.h",
     "mojo_renderer_factory.cc",