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

media/cdm/player_tracker_impl.cc

Index: media/cdm/player_tracker_impl.cc
diff --git a/media/cdm/player_tracker_impl.cc b/media/cdm/player_tracker_impl.cc
index 98f2050edefec132bb0989473dcaff63fd020382..7d5cda3bd053c31ceef9b308c8e7166ad2c16dc2 100644
--- a/media/cdm/player_tracker_impl.cc
+++ b/media/cdm/player_tracker_impl.cc
@@ -15,6 +15,9 @@ PlayerTrackerImpl::PlayerCallbacks::PlayerCallbacks(
     const base::Closure& cdm_unset_cb)
     : new_key_cb(new_key_cb), cdm_unset_cb(cdm_unset_cb) {}
 
+PlayerTrackerImpl::PlayerCallbacks::PlayerCallbacks(
+    const PlayerCallbacks& other) = default;
+
 PlayerTrackerImpl::PlayerCallbacks::~PlayerCallbacks() {
 }