Add decoder-specific settings with proper lifetime.

webrtc/config.h

Index: webrtc/config.h
diff --git a/webrtc/config.h b/webrtc/config.h
index b2dfe2d272642fa5b8f73bd4a0e75b4a3c4925d1..1550a9f8a13ac1b121c90b31a771eee56e12f1a6 100644
--- a/webrtc/config.h
+++ b/webrtc/config.h
@@ -16,6 +16,7 @@
 #include <string>
 #include <vector>
 
+#include "webrtc/base/optional.h"
 #include "webrtc/common.h"
 #include "webrtc/common_types.h"
 #include "webrtc/typedefs.h"
@@ -146,6 +147,16 @@ struct VideoEncoderConfig {
   bool expect_encode_from_texture;
 };
 
+struct VideoDecoderH264Settings {
+  std::string sprop_parameter_sets;
+};
+
+class DecoderSpecificSettings {
+ public:
+  virtual ~DecoderSpecificSettings() {}
+  rtc::Optional<VideoDecoderH264Settings> h264_extra_settings;
+};
+
 // Controls the capacity of the packet buffer in NetEq. The capacity is the
 // maximum number of packets that the buffer can contain. If the limit is
 // exceeded, the buffer will be flushed. The capacity does not affect the actual