Store Object.observe state per-isolate rather than per-context

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 76084cfd58ac23b7b3a350049830a80bb9f664ed..1440e0dc9c932fc7e922407e2dc7f08dfddb1a6f 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -2856,6 +2856,16 @@ bool Heap::CreateInitialObjects() {
   }
   set_natives_source_cache(FixedArray::cast(obj));
 
+  // Allocate object to hold object observation state.
+  Map* object_observation_map;
+  { MaybeObject* maybe_obj = AllocateMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
+    if (!maybe_obj->To(&object_observation_map)) return false;
+  }
+  { MaybeObject* maybe_obj = AllocateJSObjectFromMap(object_observation_map);
+    if (!maybe_obj->ToObject(&obj)) return false;
+  }
+  set_object_observation_state(JSObject::cast(obj));
+
   // Handling of script id generation is in FACTORY->NewScript.
   set_last_script_id(undefined_value());