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

media/base/text_track_config.h

Index: media/base/text_track_config.h
diff --git a/media/base/text_track_config.h b/media/base/text_track_config.h
index 58efba4b035f983d9d2eb82a78858c0a8b68633a..33128df99a0ec0d504331604df4f24ac8e586cd4 100644
--- a/media/base/text_track_config.h
+++ b/media/base/text_track_config.h
@@ -23,6 +23,7 @@ enum TextKind {
 class MEDIA_EXPORT TextTrackConfig {
  public:
   TextTrackConfig();
+  TextTrackConfig(const TextTrackConfig& other);
   TextTrackConfig(TextKind kind,
                   const std::string& label,
                   const std::string& language,