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 9113e7bd4058619526361c01b4482174b463b413..e3e2944ff73e18d7dbaa15b47921ba215a6d2d36 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -2852,6 +2852,15 @@ bool Heap::CreateInitialObjects() {
   }
   set_natives_source_cache(FixedArray::cast(obj));
 
+  // Allocate object to hold object observation state.
+  { MaybeObject* maybe_obj = AllocateMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
+    if (!maybe_obj->ToObject(&obj)) return false;
+  }
+  { MaybeObject* maybe_obj = AllocateJSObjectFromMap(Map::cast(obj));
+    if (!maybe_obj->ToObject(&obj)) return false;
+  }
+  set_observation_state(JSObject::cast(obj));
+
   // Handling of script id generation is in FACTORY->NewScript.
   set_last_script_id(undefined_value());