Transcoder: Added MediaTrackTranscoder and VideoTrackTranscoder

A track transcoder transcodes samples from a single track of a media file.
MediaTrackTranscoder is the base class for all track transcoder, and
VideoTrackTranscoder is a concrete implementation for video tracks.

Test: Unit test.
Bug: 152091443
Change-Id: I7980a3cda40229004b6bca5212d3e903f19a3017
diff --git a/media/libmediatranscoding/transcoder/Android.bp b/media/libmediatranscoding/transcoder/Android.bp
index e352245..44f7959 100644
--- a/media/libmediatranscoding/transcoder/Android.bp
+++ b/media/libmediatranscoding/transcoder/Android.bp
@@ -20,12 +20,15 @@
     srcs: [
         "MediaSampleQueue.cpp",
         "MediaSampleReaderNDK.cpp",
+        "MediaTrackTranscoder.cpp",
+        "VideoTrackTranscoder.cpp",
     ],
 
     shared_libs: [
         "libbase",
         "libcutils",
         "libmediandk",
+        "libnativewindow",
         "libutils",
     ],