Add more out of line copy ctors for complex classes.

mojo/edk/system/request_context.h

Index: mojo/edk/system/request_context.h
diff --git a/mojo/edk/system/request_context.h b/mojo/edk/system/request_context.h
index 394e455327499b56bb3ee0252dd7938a8ff6945a..7aa0e69b51bb2a73b1175577dec98874f5be91a9 100644
--- a/mojo/edk/system/request_context.h
+++ b/mojo/edk/system/request_context.h
@@ -67,6 +67,7 @@ class MOJO_SYSTEM_IMPL_EXPORT RequestContext {
     WatchNotifyFinalizer(scoped_refptr<Watcher> watcher,
                          MojoResult result,
                          const HandleSignalsState& state);
+    WatchNotifyFinalizer(const WatchNotifyFinalizer& other);
     ~WatchNotifyFinalizer();
 
     scoped_refptr<Watcher> watcher;