[ic] Cache weak cells containing prototypes in respective PrototypeInfo objects.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 0a1e39458bd99f1a95818424201ca0d62a3782a1..0d1eac17a780a8c400e3e644b53b4dfd98f4bf38 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6222,6 +6222,11 @@ class Map: public HeapObject {
   static const int kPrototypeChainValid = 0;
   static const int kPrototypeChainInvalid = 1;
 
+  // Returns a WeakCell object containing given prototype. The cell is cached
+  // in PrototypeInfo which is created lazily.
+  static Handle<WeakCell> GetOrCreatePrototypeWeakCell(
+      Handle<JSObject> prototype, Isolate* isolate);
+
   Map* FindRootMap();
   Map* FindFieldOwner(int descriptor);
 
@@ -6823,6 +6828,9 @@ class PrototypeInfo : public Struct {
  public:
   static const int UNREGISTERED = -1;
 
+  // [weak_cell]: A WeakCell containing this prototype. ICs cache the cell here.
+  DECL_ACCESSORS(weak_cell, Object)
+
   // [prototype_users]: WeakFixedArray containing maps using this prototype,
   // or Smi(0) if uninitialized.
   DECL_ACCESSORS(prototype_users, Object)
@@ -6856,7 +6864,8 @@ class PrototypeInfo : public Struct {
   DECLARE_PRINTER(PrototypeInfo)
   DECLARE_VERIFIER(PrototypeInfo)
 
-  static const int kPrototypeUsersOffset = HeapObject::kHeaderSize;
+  static const int kWeakCellOffset = HeapObject::kHeaderSize;
+  static const int kPrototypeUsersOffset = kWeakCellOffset + kPointerSize;
   static const int kRegistrySlotOffset = kPrototypeUsersOffset + kPointerSize;
   static const int kValidityCellOffset = kRegistrySlotOffset + kPointerSize;
   static const int kObjectCreateMap = kValidityCellOffset + kPointerSize;