[WIP] Proxy RtcVideoDecoder calls to a media::VideoDecoder.

content/public/app/mojo/content_browser_manifest.json

 {
   "manifest_version": 1,
   "name": "exe:content_browser",
   "process-group": "browser",
   "display_name": "Content Browser",
   "capabilities": {
     // Remove this once http://crbug.com/632818 is fixed.
     "provided": {
       "gpu": [ ],
       "plugin":  [ ],
@@ skipping 11 matching lines @@
         "blink::mojom::WebSocket",
         "content::mojom::MemoryCoordinatorHandle",
         "content::mojom::StoragePartitionService",
         "content::mojom::URLLoaderFactory",
         "device::BatteryMonitor",
         "device::mojom::LightSensor",
         "device::mojom::MotionSensor",
         "device::mojom::OrientationSensor",
         "device::mojom::TimeZoneMonitor",
         "media::mojom::ImageCapture",
+        "media::mojom::VideoDecoder",
         "memory_coordinator::mojom::MemoryCoordinatorHandle"
       ]
     },
     "required": {
       "*": { "classes": [ "app" ] },
 
       // In classic ash, the browser supplies ash interfaces to itself.
       "exe:content_browser": { "classes": [ "ash" ] },
 
       "exe:content_gpu": { "classes": [ "browser" ] },
@@ skipping 11 matching lines @@
       "mojo:file": {
         "interfaces": [
           "leveldb::mojom::LevelDBService",
           "user_service::UserService"
         ]
       },
       "mojo:media": { "interfaces": [ "media::mojom::MediaService" ] }
     }
   }
 }