Use FFmpegVideoDecoder from a UtilityProcess

media/media_options.gni

Index: media/media_options.gni
diff --git a/media/media_options.gni b/media/media_options.gni
index 61464d48fdee0bb4292870187f939158c2144862..5a34e81fc86c6debc00598d985303e7a79c8ae4b 100644
--- a/media/media_options.gni
+++ b/media/media_options.gni
@@ -74,7 +74,7 @@ declare_args() {
   # |mojo_media_services|). When enabled, selected mojo paths will be enabled in
   # the media pipeline and corresponding services will hosted in the selected
   # remote process (e.g. "utility" process, see |mojo_media_host|).
-  enable_mojo_media = is_android || is_chromecast
+  enable_mojo_media = is_android || is_chromecast || is_desktop_linux
 
   # Enable the TestMojoMediaClient to be used in mojo MediaService. This is for
   # testing only and will override the default platform MojoMediaClient, if any.
@@ -119,6 +119,9 @@ declare_args() {
         "renderer",
       ]
       mojo_media_host = "browser"
+    } else if (is_desktop_linux) {

[sandersd (OOO until July 31), 2016/12/15 00:38:02]

|is_desktop_linux| seems to be defined as |current_os == "linux"|. Does that
exclude chromecast?

If not, there should be a comment or condition here to make it clear that the
order of the conditions matters.

+      mojo_media_services = [ "video_decoder" ]
+      mojo_media_host = "utility"
     } else {
       mojo_media_services = [ "video_decoder" ]

[sandersd (OOO until July 31), 2016/12/15 00:38:02]

Do you plan to expand past desktop linux eventually? If so we have a problem
here, since this is the path that VDAs (DXVA, VTVDA, and the CrOS VDAs) will be
using soon.

       mojo_media_host = "gpu"