Remove support for Object.observe

src/heap/heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/scopeinfo.h"
 #include "src/base/bits.h"
@@ skipping 2743 matching lines @@
       *factory->NewFixedArray(ExtraNatives::GetBuiltinsCount()));
 
   set_experimental_extra_natives_source_cache(
       *factory->NewFixedArray(ExperimentalExtraNatives::GetBuiltinsCount()));
 
   set_undefined_cell(*factory->NewCell(factory->undefined_value()));
 
   // The symbol registry is initialized lazily.
   set_symbol_registry(Smi::FromInt(0));
 
-  // Allocate object to hold object observation state.
-  set_observation_state(*factory->NewJSObjectFromMap(
-      factory->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize)));
-
   // Microtask queue uses the empty fixed array as a sentinel for "empty".
   // Number of queued microtasks stored in Isolate::pending_microtask_count().
   set_microtask_queue(empty_fixed_array());
 
   {
     StaticFeedbackVectorSpec spec;
     FeedbackVectorSlot load_ic_slot = spec.AddLoadICSlot();
     FeedbackVectorSlot keyed_load_ic_slot = spec.AddKeyedLoadICSlot();
     FeedbackVectorSlot store_ic_slot = spec.AddStoreICSlot();
     FeedbackVectorSlot keyed_store_ic_slot = spec.AddKeyedStoreICSlot();
@@ skipping 3647 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8