Clean up decoders when stopping video receive stream.

This updates VideoReceiveStream2::Stop() to symmetrically tear down
state that's built up in VideoReceiveStream2::Start().

Bug: webrtc:11993, webrtc:14486
Change-Id: I41f4feea5584e5baaeed2143432136f8b9761321
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/272537
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38244}

modules/video_coding/decoder_database_unittest.cc

@@ -0,0 +1,75 @@
+/*
+ *  Copyright (c) 2022 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "modules/video_coding/decoder_database.h"
+
+#include "api/test/mock_video_decoder.h"
+#include "test/gmock.h"
+#include "test/gtest.h"
+
+namespace webrtc {
+namespace {
+
+using ::testing::NiceMock;
+
+// Test registering and unregistering an external decoder instance.
+TEST(VCMDecoderDataBaseTest, RegisterExternalDecoder) {
+  VCMDecoderDataBase db;
+  constexpr int kPayloadType = 1;
+  ASSERT_FALSE(db.IsExternalDecoderRegistered(kPayloadType));
+
+  NiceMock<MockVideoDecoder> decoder;
+  db.RegisterExternalDecoder(kPayloadType, &decoder);
+  EXPECT_TRUE(db.IsExternalDecoderRegistered(kPayloadType));
+  EXPECT_EQ(db.DeregisterExternalDecoder(kPayloadType), &decoder);
+  EXPECT_FALSE(db.IsExternalDecoderRegistered(kPayloadType));
+}
+
+TEST(VCMDecoderDataBaseTest, RegisterReceiveCodec) {
+  VCMDecoderDataBase db;
+  constexpr int kPayloadType = 1;
+  ASSERT_FALSE(db.DeregisterReceiveCodec(kPayloadType));
+
+  VideoDecoder::Settings settings;
+  settings.set_codec_type(kVideoCodecVP8);
+  settings.set_max_render_resolution({10, 10});
+  settings.set_number_of_cores(4);
+  db.RegisterReceiveCodec(kPayloadType, settings);
+
+  EXPECT_TRUE(db.DeregisterReceiveCodec(kPayloadType));
+}
+
+TEST(VCMDecoderDataBaseTest, DeregisterReceiveCodecs) {
+  VCMDecoderDataBase db;
+  constexpr int kPayloadType1 = 1;
+  constexpr int kPayloadType2 = 2;
+  ASSERT_FALSE(db.DeregisterReceiveCodec(kPayloadType1));
+  ASSERT_FALSE(db.DeregisterReceiveCodec(kPayloadType2));
+
+  VideoDecoder::Settings settings1;
+  settings1.set_codec_type(kVideoCodecVP8);
+  settings1.set_max_render_resolution({10, 10});
+  settings1.set_number_of_cores(4);
+
+  VideoDecoder::Settings settings2 = settings1;
+  settings2.set_codec_type(kVideoCodecVP9);
+
+  db.RegisterReceiveCodec(kPayloadType1, settings1);
+  db.RegisterReceiveCodec(kPayloadType2, settings2);
+
+  db.DeregisterReceiveCodecs();
+
+  // All receive codecs must have been removed.
+  EXPECT_FALSE(db.DeregisterReceiveCodec(kPayloadType1));
+  EXPECT_FALSE(db.DeregisterReceiveCodec(kPayloadType2));
+}
+
+}  // namespace
+}  // namespace webrtc