Add tests for %TypedArray%.prototype.sort stability (#2062)

https://github.com/tc39/ecma262/pull/1433

test/built-ins/TypedArray/stability.js

@@ -0,0 +1,45 @@
+// Copyright (C) 2019 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-%typedarray%.prototype.sort
+description: Stability of %TypedArray%.prototype.sort.
+info: |
+  https://github.com/tc39/ecma262/pull/1433
+includes: [testTypedArray.js, compareArray.js]
+features: [TypedArray]
+---*/
+
+// Treat 0..3, 4..7, etc. as equal.
+const compare = (a, b) => (a / 4 | 0) - (b / 4 | 0);
+
+testWithTypedArrayConstructors((TA) => {
+  // Create an array of the form `[0, 1, …, 126, 127]`.
+  const array = Array.from({ length: 128 }, (_, i) => i);
+
+  const typedArray1 = new TA(array);
+  assert(compareArray(
+    typedArray1.sort(compare),
+    array
+  ), 'pre-sorted');
+
+  // Reverse `array` in-place so it becomes `[127, 126, …, 1, 0]`.
+  array.reverse();
+
+  const typedArray2 = new TA(array);
+  assert(compareArray(
+    typedArray2.sort(compare),
+    [
+        3,   2,   1,   0,     7,   6,   5,   4,    11,  10,   9,   8,
+       15,  14,  13,  12,    19,  18,  17,  16,    23,  22,  21,  20,
+       27,  26,  25,  24,    31,  30,  29,  28,    35,  34,  33,  32,
+       39,  38,  37,  36,    43,  42,  41,  40,    47,  46,  45,  44,
+       51,  50,  49,  48,    55,  54,  53,  52,    59,  58,  57,  56,
+       63,  62,  61,  60,    67,  66,  65,  64,    71,  70,  69,  68,
+       75,  74,  73,  72,    79,  78,  77,  76,    83,  82,  81,  80,
+       87,  86,  85,  84,    91,  90,  89,  88,    95,  94,  93,  92,
+       99,  98,  97,  96,   103, 102, 101, 100,   107, 106, 105, 104,
+      111, 110, 109, 108,   115, 114, 113, 112,   119, 118, 117, 116,
+      123, 122, 121, 120,   127, 126, 125, 124,
+    ]
+  ), 'not presorted');
+});