[NamedLazyMemberLoading] Add "loading members" pretty stack trace when deserializing.

Author: graydon

lib/Serialization/ModuleFile.cpp

@@ -19,6 +19,7 @@
 #include "swift/AST/GenericSignature.h"
 #include "swift/AST/ModuleLoader.h"
 #include "swift/AST/NameLookup.h"
+#include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/USRGeneration.h"
 #include "swift/Basic/Range.h"
 #include "swift/ClangImporter/ClangImporter.h"
@@ -1794,6 +1795,7 @@ void ModuleFile::loadObjCMethods(
 Optional<TinyPtrVector<ValueDecl *>>
 ModuleFile::loadNamedMembers(const IterableDeclContext *IDC, DeclName N,
                              uint64_t contextData) {
+  PrettyStackTraceDecl trace("loading members for", IDC->getDecl());
 
   assert(IDC->wasDeserialized());