Throw as per spec when modifying an Array with builtin methods

src/objects.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.
 
 #include <sstream>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/allocation-site-scopes.h"
@@ skipping 13079 matching lines @@
 bool JSArray::IsReadOnlyLengthDescriptor(Handle<Map> jsarray_map) {
   Isolate* isolate = jsarray_map->GetIsolate();
   DCHECK(!jsarray_map->is_dictionary_map());
   LookupResult lookup(isolate);
   Handle<Name> length_string = isolate->factory()->length_string();
   jsarray_map->LookupDescriptor(NULL, *length_string, &lookup);
   return lookup.IsReadOnly();
 }
 
 
+bool JSArray::HasReadOnlyLength(Handle<JSArray> array) {
+  LookupIterator it(array, array->GetIsolate()->factory()->length_string(),
+                    LookupIterator::OWN_SKIP_INTERCEPTOR);
+  CHECK_NE(LookupIterator::ACCESS_CHECK, it.state());
+  CHECK(it.IsFound());
+  CHECK_EQ(LookupIterator::ACCESSOR, it.state());
+  return it.IsReadOnly();
+}
+
+
 bool JSArray::WouldChangeReadOnlyLength(Handle<JSArray> array,
                                         uint32_t index) {
   uint32_t length = 0;
   CHECK(array->length()->ToArrayIndex(&length));
-  if (length <= index) {
-    LookupIterator it(array, array->GetIsolate()->factory()->length_string(),
-                      LookupIterator::OWN_SKIP_INTERCEPTOR);
-    CHECK_NE(LookupIterator::ACCESS_CHECK, it.state());
-    CHECK(it.IsFound());
-    CHECK_EQ(LookupIterator::ACCESSOR, it.state());
-    return it.IsReadOnly();
-  }
+  if (length <= index) return HasReadOnlyLength(array);
   return false;
 }
 
 
 MaybeHandle<Object> JSArray::ReadOnlyLengthError(Handle<JSArray> array) {
   Isolate* isolate = array->GetIsolate();
   Handle<Name> length = isolate->factory()->length_string();
   Handle<Object> args[2] = { length, array };
   THROW_NEW_ERROR(isolate, NewTypeError("strict_read_only_property",
                                         HandleVector(args, arraysize(args))),
@@ skipping 3667 matching lines @@
   Handle<DependentCode> codes =
       DependentCode::Insert(handle(cell->dependent_code(), info->isolate()),
                             DependentCode::kPropertyCellChangedGroup,
                             info->object_wrapper());
   if (*codes != cell->dependent_code()) cell->set_dependent_code(*codes);
   info->dependencies(DependentCode::kPropertyCellChangedGroup)->Add(
       cell, info->zone());
 }
 
 } }  // namespace v8::internal