Add key for sample rate and bits per sample

Add new keys for sample rate and bits per sample.
This makes it possible to indicate the specification of
the music files on application.

Bug: 112986969
Test: Check if sample rate and bits per sample can be retrieved

Change-Id: Ie5a90800297a0a7c2dd6f3a2bdf9e88c9221bee1

media/java/android/media/MediaMetadataRetriever.java

@@ -958,4 +958,16 @@ public class MediaMetadataRetriever
      */
     public static final int METADATA_KEY_COLOR_RANGE    = 37;
     // Add more here...
+
+    /**
+     * This key retrieves the sample rate, if available.
+     * @hide
+     */
+    public static final int METADATA_KEY_SAMPLERATE      = 38;
+
+    /**
+     * This key retrieves the bits per sample, if available.
+     * @hide
+     */
+    public static final int METADATA_KEY_BITS_PER_SAMPLE = 39;
 }