Fixing unsafe conversion

The bot "Win (more_configs)" has spotted another unsafe type conversion.

This CL is a follow-up of:
- https://webrtc-review.googlesource.com/c/src/+/12921
- https://webrtc-review.googlesource.com/c/src/+/13122

Bug: chromium:759980
Change-Id: I3634c3e20fcd9f4e106914399ac40ca87d4c6137
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/13622
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20349}

modules/audio_coding/neteq/neteq_impl_unittest.cc

@@ -569,7 +569,7 @@ TEST_F(NetEqImplTest, ReorderedPacket) {
   EXPECT_CALL(mock_decoder, IncomingPacket(_, kPayloadLengthBytes, _, _, _))
       .WillRepeatedly(Return(0));
   EXPECT_CALL(mock_decoder, PacketDuration(_, kPayloadLengthBytes))
-      .WillRepeatedly(Return(kPayloadLengthSamples));
+      .WillRepeatedly(Return(rtc::checked_cast<int>(kPayloadLengthSamples)));
   int16_t dummy_output[kPayloadLengthSamples] = {0};
   // The below expectation will make the mock decoder write
   // |kPayloadLengthSamples| zeros to the output array, and mark it as speech.