Expose OnKeyStatusChange events, this is required to learn the usabilities of the keys.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=170268043

library/core/src/main/java/com/google/android/exoplayer2/drm/ExoMediaDrm.java

@@ -21,7 +21,9 @@ import android.media.MediaCryptoException;
 import android.media.MediaDrm;
 import android.media.MediaDrmException;
 import android.media.NotProvisionedException;
+import android.os.Handler;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.UUID;
 
@@ -80,6 +82,31 @@ public interface ExoMediaDrm<T extends ExoMediaCrypto> {
         byte[] data);
   }
 
+  /**
+   * @see android.media.MediaDrm.KeyStatus
+   */
+  interface ExoKeyStatus {
+    int getStatusCode();
+    byte[] getKeyId();
+  }
+
+  /**
+   * @see android.media.MediaDrm.OnKeyStatusChangeListener
+   */
+  interface OnKeyStatusChangeListener<T extends ExoMediaCrypto> {
+    /**
+     * Called when the keys in a session change status, such as when the license is renewed or
+     * expires.
+     *
+     * @param mediaDrm the {@link ExoMediaDrm} object on which the event occurred.
+     * @param sessionId the DRM session ID on which the event occurred.
+     * @param exoKeyInfo a list of {@link ExoKeyStatus} that contains key ID and status.
+     * @param hasNewUsableKey true if new key becomes usable.
+     */
+    void onKeyStatusChange(ExoMediaDrm<? extends T> mediaDrm, byte[] sessionId,
+        List<ExoKeyStatus> exoKeyInfo, boolean hasNewUsableKey);
+  }
+
   /**
    * @see android.media.MediaDrm.KeyRequest
    */
@@ -101,6 +128,11 @@ public interface ExoMediaDrm<T extends ExoMediaCrypto> {
    */
   void setOnEventListener(OnEventListener<? super T> listener);
 
+  /**
+   * @see MediaDrm#setOnKeyStatusChangeListener(MediaDrm.OnKeyStatusChangeListener, Handler)
+   */
+  void setOnKeyStatusChangeListener(OnKeyStatusChangeListener<? super T> listener);
+
   /**
    * @see MediaDrm#openSession()
    */

library/core/src/main/java/com/google/android/exoplayer2/drm/FrameworkMediaDrm.java

@@ -20,6 +20,7 @@ import android.media.DeniedByServerException;
 import android.media.MediaCrypto;
 import android.media.MediaCryptoException;
 import android.media.MediaDrm;
+import android.media.MediaDrm.KeyStatus;
 import android.media.MediaDrmException;
 import android.media.NotProvisionedException;
 import android.media.UnsupportedSchemeException;
@@ -27,14 +28,16 @@ import android.support.annotation.NonNull;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Util;
+import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.UUID;
 
 /**
  * An {@link ExoMediaDrm} implementation that wraps the framework {@link MediaDrm}.
  */
-@TargetApi(18)
+@TargetApi(23)
 public final class FrameworkMediaDrm implements ExoMediaDrm<FrameworkMediaCrypto> {
 
   private final UUID uuid;
@@ -71,13 +74,36 @@ public final class FrameworkMediaDrm implements ExoMediaDrm<FrameworkMediaCrypto
       final ExoMediaDrm.OnEventListener<? super FrameworkMediaCrypto> listener) {
     mediaDrm.setOnEventListener(listener == null ? null : new MediaDrm.OnEventListener() {
       @Override
-      public void onEvent(@NonNull MediaDrm md, byte[] sessionId, int event, int extra,
+      public void onEvent(@NonNull MediaDrm md, @NonNull byte[] sessionId, int event, int extra,
           byte[] data) {
         listener.onEvent(FrameworkMediaDrm.this, sessionId, event, extra, data);
       }
     });
   }
 
+  @Override
+  public void setOnKeyStatusChangeListener(
+      final ExoMediaDrm.OnKeyStatusChangeListener<? super FrameworkMediaCrypto> listener) {
+    if (Util.SDK_INT < 23) {
+      throw new UnsupportedOperationException();
+    }
+    
+    mediaDrm.setOnKeyStatusChangeListener(listener == null ? null
+        : new MediaDrm.OnKeyStatusChangeListener() {
+          @Override
+          public void onKeyStatusChange(@NonNull MediaDrm md, @NonNull byte[] sessionId,
+              @NonNull List<KeyStatus> keyInfo, boolean hasNewUsableKey) {
+            List<ExoKeyStatus> exoKeyInfo = new ArrayList<>();
+            for (KeyStatus keyStatus : keyInfo) {
+              exoKeyInfo.add(new FrameworkKeyStatus(keyStatus));
+            }
+
+            listener.onKeyStatusChange(FrameworkMediaDrm.this, sessionId, exoKeyInfo,
+                hasNewUsableKey);
+          }
+        }, null);
+  }
+
   @Override
   public byte[] openSession() throws MediaDrmException {
     return mediaDrm.openSession();
@@ -178,4 +204,22 @@ public final class FrameworkMediaDrm implements ExoMediaDrm<FrameworkMediaCrypto
         forceAllowInsecureDecoderComponents);
   }
 
+  private static final class FrameworkKeyStatus implements ExoKeyStatus {
+    private final MediaDrm.KeyStatus keyStatus;
+
+    FrameworkKeyStatus(MediaDrm.KeyStatus keyStatus) {
+      this.keyStatus = keyStatus;
+    }
+
+    @Override
+    public int getStatusCode() {
+      return keyStatus.getStatusCode();
+    }
+
+    @Override
+    public byte[] getKeyId() {
+      return keyStatus.getKeyId();
+    }
+  }
+
 }