Clear out cached codecs when calculating new codec lists.

webrtc/media/engine/webrtcvideoencoderfactory_unittest.cc

+/*
+ *  Copyright (c) 2017 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 "webrtc/media/engine/webrtcvideoencoderfactory.h"
+
+#include "webrtc/test/gtest.h"
+
+class WebRtcVideoEncoderFactoryForTest
+    : public cricket::WebRtcVideoEncoderFactory {
+ public:
+  WebRtcVideoEncoderFactoryForTest() {
+    codecs_.push_back(VideoCodec(webrtc::kVideoCodecH264, "H264"));
+    codecs_.push_back(VideoCodec(webrtc::kVideoCodecVP8, "VP8"));
+  }
+
+  const std::vector<VideoCodec>& codecs() const override { return codecs_; }
+
+  void DestroyVideoEncoder(webrtc::VideoEncoder* encoder) override {}
+
+  std::vector<VideoCodec> codecs_;
+};
+
+TEST(WebRtcVideoEncoderFactoryTest, TestMultipleCallsToSupportedCodecs) {
+  WebRtcVideoEncoderFactoryForTest factory;
+  EXPECT_EQ(2u, factory.supported_codecs().size());
+  EXPECT_EQ("H264", factory.supported_codecs()[0].name);
+  EXPECT_EQ("VP8", factory.supported_codecs()[1].name);
+
+  // The codec list doesn't grow when called repeatedly.
+  EXPECT_EQ(2u, factory.supported_codecs().size());
+}