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

media/base/audio_shifter.cc

Index: media/base/audio_shifter.cc
diff --git a/media/base/audio_shifter.cc b/media/base/audio_shifter.cc
index c88af3ac2304f0247e403ae91348deba03fb60bf..6a268d3f6339d5bd6fee07966494f3dd1b66f301 100644
--- a/media/base/audio_shifter.cc
+++ b/media/base/audio_shifter.cc
@@ -82,6 +82,9 @@ AudioShifter::AudioQueueEntry::AudioQueueEntry(
     audio(audio_.release()) {
 }
 
+AudioShifter::AudioQueueEntry::AudioQueueEntry(const AudioQueueEntry& other) =
+    default;
+
 AudioShifter::AudioQueueEntry::~AudioQueueEntry() {}
 
 AudioShifter::AudioShifter(base::TimeDelta max_buffer_size,