Remove the --collect-maps flag. Maps should be always collected.

src/heap/objects-visiting-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_VISITING_INL_H_
 #define V8_OBJECTS_VISITING_INL_H_
 
 #include "src/heap/objects-visiting.h"
 
 namespace v8 {
@@ skipping 280 matching lines @@
   Heap* heap = map->GetHeap();
   Map* map_object = Map::cast(object);
 
   // Clears the cache of ICs related to this map.
   if (FLAG_cleanup_code_caches_at_gc) {
     map_object->ClearCodeCache(heap);
   }
 
   // When map collection is enabled we have to mark through map's transitions
   // and back pointers in a special way to make these links weak.
-  if (FLAG_collect_maps && map_object->CanTransition()) {
+  if (map_object->CanTransition()) {
     MarkMapContents(heap, map_object);
   } else {
     StaticVisitor::VisitPointers(
         heap, HeapObject::RawField(object, Map::kPointerFieldsBeginOffset),
         HeapObject::RawField(object, Map::kPointerFieldsEndOffset));
   }
 }
 
 
 template <typename StaticVisitor>
@@ skipping 519 matching lines @@
 
   RelocIterator it(this, mode_mask);
   for (; !it.done(); it.next()) {
     it.rinfo()->template Visit<StaticVisitor>(heap);
   }
 }
 }
 }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_VISITING_INL_H_