Add ExoPlayerDemo.apk to vendor/widevine so partners can access

it and use to verify integrations.

bug: 11357407

Change-Id: Ie38cef1dfd2fe685721e7fb4f37e881326321727

libwvdrmengine/test/demo/readme.txt

@@ -0,0 +1,28 @@
+ExoPlayerDemo.apk can be used to do end-to-end verification of your Modular DRM.
+
+To install, side load ExoPlayerDemo.apk app to your device:
+
+  adb install ExoPlayerDemo.apk
+
+To run, launch ExoPlayer, then choose the Revenge (DASH CENC) clip, which is encrypted
+   using DASH Common Encryption.  Then press "Play" to start playback.  The other clips
+   in the list are clear (i.e. not encrypted).
+
+Notes:
+
+- The demo app shows up in the launcher as "ExoPlayer"
+
+- The demo app contains a crude adaptive algorithm. It starts at 144p and will not switch up for 15
+  seconds. This is expected (and has the benefit of more or less guaranteeing there's at least one
+  switch during any playback beyond this length).
+
+- If your device is running KLP, and the decoder claims to support adaptive, then ExoPlayer will
+  do seamless resolution switching. If the decoder doesn't claim this then you'll still get the
+  old nearly-seamless-switch (codec release/re-acquire) behavior.
+
+- If your device is running KLP, the player will attempt to hook into the new
+  AudioTrack.getTimestamp API to do A/V sync. It will fall back to how it used to do things if
+  the API isn't available.
+
+- The apk is still built against API level 18. The features above are accessed via reflection.
+