Add fake shuffle order.

This just implements a reverse order which is different from the original order but
still deterministic for simplified testing.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=166194311

testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeShuffleOrder.java

@@ -0,0 +1,68 @@
+/*
+ * 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.testutil;
+
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.source.ShuffleOrder;
+
+/**
+ * Fake {@link ShuffleOrder} which returns a reverse order. This order is thus deterministic but
+ * different from the original order.
+ */
+public final class FakeShuffleOrder implements ShuffleOrder {
+
+  private final int length;
+
+  public FakeShuffleOrder(int length) {
+    this.length = length;
+  }
+
+  @Override
+  public int getLength() {
+    return length;
+  }
+
+  @Override
+  public int getNextIndex(int index) {
+    return index > 0 ? index - 1 : C.INDEX_UNSET;
+  }
+
+  @Override
+  public int getPreviousIndex(int index) {
+    return index < length - 1 ? index + 1 : C.INDEX_UNSET;
+  }
+
+  @Override
+  public int getLastIndex() {
+    return length > 0 ? 0 : C.INDEX_UNSET;
+  }
+
+  @Override
+  public int getFirstIndex() {
+    return length > 0 ? length - 1 : C.INDEX_UNSET;
+  }
+
+  @Override
+  public ShuffleOrder cloneAndInsert(int insertionIndex, int insertionCount) {
+    return new FakeShuffleOrder(length + insertionCount);
+  }
+
+  @Override
+  public ShuffleOrder cloneAndRemove(int removalIndex) {
+    return new FakeShuffleOrder(length - 1);
+  }
+
+}