Use SetOwnElement when creating splice records in array length setter

This avoids touching the Array prototype, which may have been tampered with.

BUG=chromium:443982
LOG=n

Review URL: https://codereview.chromium.org/820503005

Cr-Commit-Position: refs/heads/master@{#25908}

src/objects.cc

@@ -11809,8 +11809,8 @@ MaybeHandle<Object> JSArray::SetElementsLength(
       // Skip deletions where the property was an accessor, leaving holes
       // in the array of old values.
       if (old_values[i]->IsTheHole()) continue;
-      JSObject::SetElement(
-          deleted, indices[i] - index, old_values[i], NONE, SLOPPY).Assert();
+      JSObject::SetOwnElement(deleted, indices[i] - index, old_values[i],
+                              SLOPPY).Assert();
     }
 
     SetProperty(deleted, isolate->factory()->length_string(),

test/mjsunit/es7/regress/regress-443982.js

+// Copyright 2014 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.
+
+var records;
+function observer(r) {
+  records = r;
+}
+
+Object.defineProperty(Array.prototype, '0', {
+  get: function() { return 0; },
+  set: function() { throw "boom!"; }
+});
+arr = [1, 2];
+Array.observe(arr, observer);
+arr.length = 0;
+assertEquals(0, arr.length);
+
+Object.deliverChangeRecords(observer);
+assertEquals(1, records.length);
+assertEquals('splice', records[0].type);
+assertArrayEquals([1, 2], records[0].removed);