Reland [typedarrays] move %TypedArray%.prototype.copyWithin to C++

test/mjsunit/es6/regress/regress-5929-1.js

+// Copyright 2017 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.
+
+// Flags: --allow-natives-syntax
+
+var buf = new ArrayBuffer(0x10000);
+var arr = new Uint8Array(buf).fill(55);
+var tmp = {};
+tmp[Symbol.toPrimitive] = function () {
+  %ArrayBufferNeuter(arr.buffer);
+  return 50;
+}
+arr.copyWithin(tmp);

[Dan Ehrenberg, 2017/02/13 19:56:44]

Could you test that this leaves the TypedArray in a detached-looking state?

Also, apparently we're missing a test that copyWithin on a detached TypedArray
does nothing; it'd be good to add it (this is actually my fault, but you're
rewriting code which hits that path, so it'd be good to have a test to confirm).

[Camillo Bruni, 2017/02/13 20:18:56]

This should throw as you will start iterating from 50 to 0x10000, since you call
[[HasProperty]] (22.1.3.3 12.c) which will trow if detached (see 9.4.5.2 3.ii).

[caitp, 2017/02/13 20:21:55]

It should, but it's been suggested that we make all the TypedArray operations
throw at the same time, to prevent giving TC39 an excuse to make a very
complicated set of rules about when to throw and when not to.

So, coming in the next patch set, both the detached-before-call and
detached-during-ToInteger cases will just cause an early exit