Move VideoStreamReceiver JSON configuration parser to test source_set.

This change moves the configuration parser that converts a JSON representation
of the VideoStreamReceiver::Config structure into a native object into the test
directory so that it can be shared with the new corpus_generator utility that is
being built. This rtc_source_set will have an additional utility function added
in a subsequent CL that will allow the generation of a VideoStreamSender::Config
from a given VideoStreamReceiver::Config and visa versa.

Bug: webrtc:10117
Change-Id: I3035826f799f8d1fcdeaa76997391f030c855a5c
Reviewed-on: https://webrtc-review.googlesource.com/c/116880
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Benjamin Wright <benwright@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26252}

test/call_config_utils.h

@@ -0,0 +1,29 @@
+/*
+ *  Copyright (c) 2019 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.
+ */
+
+#ifndef TEST_CALL_CONFIG_UTILS_H_
+#define TEST_CALL_CONFIG_UTILS_H_
+
+#include "call/video_receive_stream.h"
+#include "rtc_base/strings/json.h"
+
+namespace webrtc {
+namespace test {
+
+// Deserializes a JSON representation of the VideoReceiveStream::Config back
+// into a valid object. This will not initialize the decoders or the renderer.
+VideoReceiveStream::Config ParseVideoReceiveStreamJsonConfig(
+    webrtc::Transport* transport,
+    const Json::Value& json);
+
+}  // namespace test
+}  // namespace webrtc
+
+#endif  // TEST_CALL_CONFIG_UTILS_H_