Add super-simple SimpleExoPlayer factory method.

The DefaultTrackSelector can now be constructed without leaving out a
vital part of the initialization. This allows this new simple factory method.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=213438163

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java

@@ -22,6 +22,7 @@ import com.google.android.exoplayer2.analytics.AnalyticsCollector;
 import com.google.android.exoplayer2.audio.AudioAttributes;
 import com.google.android.exoplayer2.drm.DrmSessionManager;
 import com.google.android.exoplayer2.drm.FrameworkMediaCrypto;
+import com.google.android.exoplayer2.trackselection.DefaultTrackSelector;
 import com.google.android.exoplayer2.trackselection.TrackSelector;
 import com.google.android.exoplayer2.upstream.BandwidthMeter;
 import com.google.android.exoplayer2.upstream.DefaultBandwidthMeter;
@@ -135,6 +136,15 @@ public final class ExoPlayerFactory {
    * Creates a {@link SimpleExoPlayer} instance.
    *
    * @param context A {@link Context}.
+   */
+  public static SimpleExoPlayer newSimpleInstance(Context context) {
+    return newSimpleInstance(context, new DefaultTrackSelector());
+  }
+
+  /**
+   * Creates a {@link SimpleExoPlayer} instance.
+   *
+   * @param context A {@link Context}.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
    */
   public static SimpleExoPlayer newSimpleInstance(Context context, TrackSelector trackSelector) {