message: Add unit test for BufQueue::clone
  Summary: As titled.
diff: @@ -176,6 +176,28 @@ TEST(BufQueue, TrimStartAtMost) {
  checkConsistency(queue);
  }
  +TEST(BufQueue, CloneBufNull) {
  + BufQueue queue;
  + auto buf = queue.clone();
  + EXPECT_EQ(nullptr, buf);
  +}
  +
  +TEST(BufQueue, CloneBuf) {
  + std::string s("Hello, World");
  + BufQueue queue;
  + queue.append(IOBuf::copyBuffer(s.data(), s.length()));
  + auto buf = queue.clone();
  + const IOBuf* chain = queue.front();
  + EXPECT_EQ(s.length(), chain->computeChainDataLength());
  + EXPECT_EQ(s.length(), buf->computeChainDataLength());
  + EXPECT_EQ(0, memcmp(chain->data(), buf->data(), s.length()));
  + queue.append(IOBuf::copyBuffer(s.data(), s.length()));
  + EXPECT_EQ(2 * s.length(), chain->computeChainDataLength());
  + EXPECT_EQ(s.length(), buf->computeChainDataLength());
  + buf = queue.clone();
  + EXPECT_EQ(2 * s.length(), buf->computeChainDataLength());
  +}
  +
  TEST(BufAppender, TestPushAlreadyFits) {
  std::unique_ptr<folly::IOBuf> data = folly::IOBuf::create(10);
  BufAppender appender(data.get(), 10);
  