Related PR : #5691
The result of `TopKSelector` may be wrong when `trim()` is invoked and quiksort fallback to `Arrasys.sort()`. Because `Arrasys.sort()` is been used by mistake there.
Following test case can trigger this bug.
```
{
    int n = 10000;
    int k = 10000;
    int testIteration = 10;
    Random random = new Random(System.currentTimeMillis());
    for (int iter = 0; iter < testIteration; iter ++) {
      // target array to be sorted using TopKSelector
      List<Integer> target = new ArrayList<>();
      for (int i = 0; i < 9; i++) {
        List<Integer> sortedArray = new ArrayList();
        for (int j = 0; j < n; j++) {
          sortedArray.add(random.nextInt());
        }
        sortedArray.sort(Integer::compareTo);
        target.addAll(sortedArray);
      }

      TopKSelector<Integer> top = TopKSelector.least(k, Integer::compareTo);
      for (int value : target) {
        top.offer(value);
      }

      target.sort(Integer::compareTo);
      assertEquals(top.topK(), target.subList(0, k));
    }
  }
```
/*
 * Copyright (C) 2014 The Guava Authors
 *
 * 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.common.collect;
import static com.google.common.truth.Truth.assertThat;
import com.google.common.math.IntMath;
import com.google.common.primitives.Ints;
import java.math.RoundingMode;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import junit.framework.TestCase;
/**
 * Tests for {@code TopKSelector}.
 *
 * @author Louis Wasserman
 */
public class TopKSelectorTest extends TestCase {