Merge pull request #1504 from jswalden/dv-final-detachment-check

Add a test verifying that the OrdinaryCreateFromConstructor call in the DataView constructor is checked for underlying-buffer detachedness before its result is used

test/built-ins/DataView/custom-proto-access-detaches-buffer.js

+// Copyright (C) 2018 Mozilla Corporation. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+author: Jeff Walden <jwalden+code@mit.edu>
+esid: sec-dataview-buffer-byteoffset-bytelength
+description: >
+  The `DataView` constructor shouldn't be able to return a `DataView` instance
+  backed by a detached `ArrayBuffer` when `OrdinaryCreateFromConstructor`
+  returns an instance so backed.
+info: |
+  `OrdinaryCreateFromConstructor` has the potential to invoke user-defined code
+  that may detach the `ArrayBuffer` intended to underlie the fresh instance.
+  Verify that a final is-detached check is performed before the new instance is
+  returned.
+features: [Reflect.construct]
+---*/
+
+var buffer = new ArrayBuffer(8);
+
+var called = false;
+var byteOffset = { valueOf() { called = true; return 0; } };
+
+var newTarget = function() {}.bind(null);
+Object.defineProperty(newTarget, "prototype", {
+  get() {
+    $262.detachArrayBuffer(buffer);
+    return DataView.prototype;
+  }
+});
+
+assert.throws(TypeError, function() {
+  Reflect.construct(DataView, [buffer, byteOffset], newTarget);
+});
+assert.sameValue(called, true);