Implement immutable prototype chains

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 72ca092f5123c0f4920b17bba638594b49612c17..fa90b0689a35129ca0bf0898637ecf4a9f968fa6 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
+  MUST_USE_RESULT static Maybe<bool> SetImmutableProto(
+      Handle<JSObject> object, bool from_javascript, ShouldThrow should_throw);
+
   // 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.
@@ -5703,7 +5707,7 @@ 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.
 
@@ -5991,6 +5995,8 @@ 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();
@@ -6163,6 +6169,8 @@ class Map: public HeapObject {
                                            Handle<Object> prototype,
                                            PrototypeOptimizationMode mode);
 
+  static Handle<Map> TransitionToImmutableProto(Handle<Map> map);
+
   static const int kMaxPreAllocatedPropertyFields = 255;
 
   // Layout description.
@@ -10685,7 +10693,9 @@ 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)
 
@@ -10694,9 +10704,9 @@ 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;
 };