Remove support for Object.observe

src/ic/arm64/ic-arm64.cc

 // Copyright 2013 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.
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/codegen.h"
 #include "src/ic/ic.h"
 #include "src/ic/ic-compiler.h"
 #include "src/ic/stub-cache.h"
@@ skipping 604 matching lines @@
   DCHECK(value.is(x0));
 
   Register receiver_map = x3;
   Register elements = x4;
   Register elements_map = x5;
 
   __ JumpIfNotSmi(key, &maybe_name_key);
   __ JumpIfSmi(receiver, &slow);
   __ Ldr(receiver_map, FieldMemOperand(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.
   __ Ldrb(x10, FieldMemOperand(receiver_map, Map::kBitFieldOffset));
-  __ TestAndBranchIfAnySet(
-      x10, (1 << Map::kIsAccessCheckNeeded) | (1 << Map::kIsObserved), &slow);
+  __ TestAndBranchIfAnySet(x10, (1 << Map::kIsAccessCheckNeeded), &slow);
 
   // Check if the object is a JS array or not.
   Register instance_type = x10;
   __ CompareInstanceType(receiver_map, instance_type, JS_ARRAY_TYPE);
   __ B(eq, &array);
   // Check that the object is some kind of JS object EXCEPT JS Value type. In
   // the case that the object is a value-wrapper object, we enter the runtime
   // system to make sure that indexing into string objects works as intended.
   STATIC_ASSERT(JS_VALUE_TYPE < JS_OBJECT_TYPE);
   __ Cmp(instance_type, JS_OBJECT_TYPE);
@@ skipping 218 matching lines @@
   } else {
     DCHECK(to_patch->Mask(TestBranchMask) == TBNZ);
     // This is JumpIfSmi(smi_reg, branch_imm).
     patcher.tbz(smi_reg, 0, branch_imm);
   }
 }
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM64