Implement immutable prototype chains

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index a8a07c0a47f512f8c18a36715a34c06795743e7b..9e8f5c0a221729d60f829d115e2edf31cdb51c28 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2346,6 +2346,10 @@ class JSObject: public JSReceiver {
                                                   bool from_javascript,
                                                   ShouldThrow should_throw);
 
+  // Makes the object prototype immutable
+  // Never called from JavaScript
+  static void SetImmutableProto(Handle<JSObject> object);
+
   // Initializes the body starting at |start_offset|. It is responsibility of
   // the caller to initialize object header. Fill the pre-allocated fields with
   // pre_allocated_value and the rest with filler_value.
@@ -5702,7 +5706,7 @@ class Map: public HeapObject {
   class Deprecated : public BitField<bool, 23, 1> {};
   class IsUnstable : public BitField<bool, 24, 1> {};
   class IsMigrationTarget : public BitField<bool, 25, 1> {};
-  // Bit 26 is free.
+  class ImmutablePrototype : public BitField<bool, 26, 1> {};
   class NewTargetIsBase : public BitField<bool, 27, 1> {};
   // Bit 28 is free.
 
@@ -5990,6 +5994,8 @@ class Map: public HeapObject {
   inline bool is_stable();
   inline void set_migration_target(bool value);
   inline bool is_migration_target();
+  inline void set_immutable_proto(bool value);
+  inline bool is_immutable_proto();
   inline void set_construction_counter(int value);
   inline int construction_counter();
   inline void deprecate();
@@ -6162,6 +6168,8 @@ class Map: public HeapObject {
                                            Handle<Object> prototype,
                                            PrototypeOptimizationMode mode);
 
+  static Handle<Map> TransitionToImmutableProto(Handle<Map> map);
+
   static const int kMaxPreAllocatedPropertyFields = 255;
 
   // Layout description.
@@ -10708,7 +10716,9 @@ class FunctionTemplateInfo: public TemplateInfo {
 class ObjectTemplateInfo: public TemplateInfo {
  public:
   DECL_ACCESSORS(constructor, Object)
-  DECL_ACCESSORS(internal_field_count, Object)
+  DECL_ACCESSORS(data, Object)
+  DECL_INT_ACCESSORS(internal_field_count)
+  DECL_BOOLEAN_ACCESSORS(immutable_proto)
 
   DECLARE_CAST(ObjectTemplateInfo)
 
@@ -10717,9 +10727,14 @@ class ObjectTemplateInfo: public TemplateInfo {
   DECLARE_VERIFIER(ObjectTemplateInfo)
 
   static const int kConstructorOffset = TemplateInfo::kHeaderSize;
-  static const int kInternalFieldCountOffset =
-      kConstructorOffset + kPointerSize;
-  static const int kSize = kInternalFieldCountOffset + kPointerSize;
+  // LSB is for immutable_proto, higher bits for internal_field_count
+  static const int kDataOffset = kConstructorOffset + kPointerSize;
+  static const int kSize = kDataOffset + kPointerSize;
+
+ private:
+  class IsImmutablePrototype : public BitField<bool, 0, 1> {};
+  class InternalFieldCount
+      : public BitField<int, IsImmutablePrototype::kNext, 29> {};
 };