Provide setPlaybackParams convenience method.

It's not a comprehensive solution for setting the
playback speed because (a) it doesn't apply when
audio is disabled, and (b) we do some timestamp
interpolation in a few places where we assume real
time. However in practice it works pretty well and
most apps probably don't allow disabling of audio,
so I think it makes sense to expose it.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=123406605

library/src/main/java/com/google/android/exoplayer/SimpleExoPlayer.java

@@ -31,6 +31,7 @@ import android.annotation.TargetApi;
 import android.content.Context;
 import android.media.AudioManager;
 import android.media.MediaCodec;
+import android.media.PlaybackParams;
 import android.os.Handler;
 import android.util.Log;
 import android.view.Surface;
@@ -195,6 +196,22 @@ public final class SimpleExoPlayer implements ExoPlayer {
   }
 
   /**
+   * Sets {@link PlaybackParams} governing audio playback.
+   *
+   * @param params The {@link PlaybackParams}.
+   */
+  public void setPlaybackParams(PlaybackParams params) {
+    ExoPlayerMessage[] messages = new ExoPlayerMessage[audioRendererCount];
+    int count = 0;
+    for (TrackRenderer renderer : renderers) {
+      if (renderer.getTrackType() == C.TRACK_TYPE_AUDIO) {
+        messages[count++] = new ExoPlayerMessage(renderer, C.MSG_SET_PLAYBACK_PARAMS, params);
+      }
+    }
+    player.sendMessages(messages);
+  }
+
+  /**
    * @return The {@link BandwidthMeter} being used by the player.
    */
   public BandwidthMeter getBandwidthMeter() {