DecryptionException cleanup + add missing header

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=167711928

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

@@ -1,20 +1,37 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 package com.google.android.exoplayer2.drm;
 
 /**
- * An exception when doing drm decryption using the In-App Drm
+ * Thrown when a non-platform component fails to decrypt data.
  */
 public class DecryptionException extends Exception {
-  private final int errorCode;
 
+  /**
+   * A component specific error code.
+   */
+  public final int errorCode;
+
+  /**
+   * @param errorCode A component specific error code.
+   * @param message The detail message.
+   */
   public DecryptionException(int errorCode, String message) {
     super(message);
     this.errorCode = errorCode;
   }
 
-  /**
-   * Get error code
-   */
-  public int getErrorCode() {
-    return errorCode;
-  }
 }

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

@@ -28,7 +28,9 @@ import java.util.Map;
 @TargetApi(16)
 public interface DrmSession<T extends ExoMediaCrypto> {
 
-  /** Wraps the throwable which is the cause of the error state. */
+  /**
+   * Wraps the throwable which is the cause of the error state.
+   */
   class DrmSessionException extends Exception {
 
     public DrmSessionException(Throwable cause) {