Remove support for Object.observe

src/ic/x64/ic-x64.cc

Index: src/ic/x64/ic-x64.cc
diff --git a/src/ic/x64/ic-x64.cc b/src/ic/x64/ic-x64.cc
index 5b9fdcf9042092eca854706a7c478d5ea590abb6..4e9927d12d8cd4799a932805b7fcb582c4f2f4f0 100644
--- a/src/ic/x64/ic-x64.cc
+++ b/src/ic/x64/ic-x64.cc
@@ -519,10 +519,10 @@ void KeyedStoreIC::GenerateMegamorphic(MacroAssembler* masm,
   __ JumpIfSmi(receiver, &slow_with_tagged_index);
   // Get the map from the receiver.
   __ movp(r9, FieldOperand(receiver, HeapObject::kMapOffset));
-  // Check that the receiver does not require access checks and is not observed.
-  // The generic stub does not perform map checks or handle observed objects.
+  // Check that the receiver does not require access checks.
+  // The generic stub does not perform map checks.
   __ testb(FieldOperand(r9, Map::kBitFieldOffset),
-           Immediate(1 << Map::kIsAccessCheckNeeded | 1 << Map::kIsObserved));
+           Immediate(1 << Map::kIsAccessCheckNeeded));
   __ j(not_zero, &slow_with_tagged_index);
   // Check that the key is a smi.
   __ JumpIfNotSmi(key, &maybe_name_key);