Add support for per-isolate private symbols

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 0691947600c1923049eb3e02fa65422c5b2d369e..af51f28fb15e33f8e60d24f7e22d78faef9e5b8d 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -3288,13 +3288,8 @@ bool Heap::CreateInitialObjects() {
   }
   set_undefined_cell(Cell::cast(obj));
 
-  // Allocate objects to hold symbol registry.
-  { MaybeObject* maybe_obj = AllocateMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
-    if (!maybe_obj->ToObject(&obj)) return false;
-    maybe_obj = AllocateJSObjectFromMap(Map::cast(obj));
-    if (!maybe_obj->ToObject(&obj)) return false;
-  }
-  set_symbol_registry(JSObject::cast(obj));
+  // The symbol registry is initialized lazily.
+  set_symbol_registry(undefined_value());
 
   // Allocate object to hold object observation state.
   { MaybeObject* maybe_obj = AllocateMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);