media: Add out-of-line copy ctors for complex classes.

media/base/video_decoder_config.cc

Index: media/base/video_decoder_config.cc
diff --git a/media/base/video_decoder_config.cc b/media/base/video_decoder_config.cc
index dfe7254e9aff1919d7cd0c442eed5df11b20faac..930ffd95d0855abb01e2f5701f693826e24d7246 100644
--- a/media/base/video_decoder_config.cc
+++ b/media/base/video_decoder_config.cc
@@ -55,6 +55,9 @@ VideoDecoderConfig::VideoDecoderConfig(VideoCodec codec,
              natural_size, extra_data, is_encrypted);
 }
 
+VideoDecoderConfig::VideoDecoderConfig(const VideoDecoderConfig& other) =
+    default;
+
 VideoDecoderConfig::~VideoDecoderConfig() {}
 
 void VideoDecoderConfig::Initialize(VideoCodec codec,