Refactor copying of maps and descriptor arrays.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index b7d9da3ffd1fe551fec74fbc8da6a888486ce7a4..89d28099f69cf6595b364a4948e82057a7ea9b95 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -4910,7 +4910,11 @@ class Map: public HeapObject {
                                     String* name,
                                     LookupResult* result);
 
+  MUST_USE_RESULT MaybeObject* RawCopy(int instance_size);
+  MUST_USE_RESULT MaybeObject* CopyWithPreallocatedFieldDescriptors();
   MUST_USE_RESULT MaybeObject* CopyDropDescriptors();
+  MUST_USE_RESULT MaybeObject* CopyReplaceDescriptors(
+      DescriptorArray* descriptors);
 
   MUST_USE_RESULT MaybeObject* CopyNormalized(PropertyNormalizationMode mode,
                                               NormalizedMapSharingMode sharing);