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

base/task_scheduler/priority_queue.h

Index: base/task_scheduler/priority_queue.h
diff --git a/base/task_scheduler/priority_queue.h b/base/task_scheduler/priority_queue.h
index 36c4bd9af83553358cf13b1eb1aaab9ca2e05c1b..8676c932c75e5906e14f1527e2e2a86ef16501be 100644
--- a/base/task_scheduler/priority_queue.h
+++ b/base/task_scheduler/priority_queue.h
@@ -33,6 +33,8 @@ class BASE_EXPORT PriorityQueue {
     SequenceAndSortKey(scoped_refptr<Sequence> sequence,
                        const SequenceSortKey& sort_key);
 
+    SequenceAndSortKey(const SequenceAndSortKey& other);
+
     ~SequenceAndSortKey();
 
     // Returns true if this is a null SequenceAndSortKey.