Partially revert r29468

BUG=chromium:507767
LOG=n

Review URL: https://codereview.chromium.org/1224853003

Cr-Commit-Position: refs/heads/master@{#29528}

src/objects-inl.h

@@ -6946,12 +6946,13 @@ void Map::ClearCodeCache(Heap* heap) {
 }
 
 
-int Map::SlackForArraySize(bool is_prototype_map, int old_size,
-                           int size_limit) {
+int Map::SlackForArraySize(int old_size, int size_limit) {
   const int max_slack = size_limit - old_size;
   CHECK_LE(0, max_slack);
-  if (old_size < 4) return Min(max_slack, 1);
-  if (is_prototype_map) return Min(max_slack, 4);
+  if (old_size < 4) {
+    DCHECK_LE(1, max_slack);
+    return 1;
+  }
   return Min(max_slack, old_size / 4);
 }
 

src/objects.cc

@@ -6762,8 +6762,7 @@ Handle<Map> Map::ShareDescriptor(Handle<Map> map,
     if (old_size == 0) {
       descriptors = DescriptorArray::Allocate(map->GetIsolate(), 0, 1);
     } else {
-      int slack = SlackForArraySize(map->is_prototype_map(), old_size,
-                                    kMaxNumberOfDescriptors);
+      int slack = SlackForArraySize(old_size, kMaxNumberOfDescriptors);
       EnsureDescriptorSlack(map, slack);
       descriptors = handle(map->instance_descriptors());
     }

src/objects.h

@@ -6027,8 +6027,7 @@ class Map: public HeapObject {
   static void AppendCallbackDescriptors(Handle<Map> map,
                                         Handle<Object> descriptors);
 
-  static inline int SlackForArraySize(bool is_prototype_map, int old_size,
-                                      int size_limit);
+  static inline int SlackForArraySize(int old_size, int size_limit);
 
   static void EnsureDescriptorSlack(Handle<Map> map, int slack);
 

src/transitions.cc

@@ -106,10 +106,9 @@ void TransitionArray::Insert(Handle<Map> map, Handle<Name> name,
   }
 
   // We're gonna need a bigger TransitionArray.
-  Handle<TransitionArray> result =
-      Allocate(map->GetIsolate(), new_nof,
-               Map::SlackForArraySize(false, number_of_transitions,
-                                      kMaxNumberOfTransitions));
+  Handle<TransitionArray> result = Allocate(
+      map->GetIsolate(), new_nof,
+      Map::SlackForArraySize(number_of_transitions, kMaxNumberOfTransitions));
 
   // The map's transition array may have shrunk during the allocation above as
   // it was weakly traversed, though it is guaranteed not to disappear. Trim the