[js-perf-tests] Fix micro-benchmark of spreading double arrays.

Array.prototype.map is currently not preserving PACKEDness. Use a
for-loop instead.

Bug: v8:7980
Change-Id: I08aff1cbcd84b9de260a5a1e2c68b9cfb5c3d888
Reviewed-on: https://chromium-review.googlesource.com/c/1280329
Commit-Queue: Hai Dang <dhai@google.com>
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56657}

test/js-perf-test/ArrayLiteralInitialSpreadLargeDoublePacked/run.js

@@ -5,8 +5,12 @@
 // Comparing different copy schemes against spread initial literals.
 // Benchmarks for large packed double arrays.
 
-const largeHoleyArray = new Array(1e5);
-const largeArray = Array.from(largeHoleyArray.keys()).map(x => x + 6.66);
+var largeArray = Array.from(Array(1e5).keys());
+// TODO(dhai): we should be able to use Array.prototype.map here, but that
+// implementation is currently creating a HOLEY array.
+for (var i = 0; i < 1e5; i++) {
+  largeArray[i] += 6.66;
+}
 
 // ----------------------------------------------------------------------------
 // Benchmark: Spread

test/js-perf-test/ArrayLiteralInitialSpreadLargePacked/run.js

@@ -5,8 +5,7 @@
 // Comparing different copy schemes against spread initial literals.
 // Benchmarks for large packed arrays.
 
-const largeHoleyArray = new Array(1e5);
-const largeArray = Array.from(largeHoleyArray.keys());
+const largeArray = Array.from(Array(1e5).keys());
 
 // ----------------------------------------------------------------------------
 // Benchmark: Spread

test/js-perf-test/ArrayLiteralInitialSpreadSmallDoublePacked/run.js

@@ -5,8 +5,12 @@
 // Comparing different copy schemes against spread initial literals.
 // Benchmarks for small packed double arrays.
 
-const smallHoleyArray = Array(100);
-const smallArray = Array.from(Array(100).keys()).map(x => x + 6.66);;
+var smallArray = Array.from(Array(100).keys());
+
+for (var i = 0; i < 100; i++) {
+  smallArray[i] += 6.66;
+}
+
 
 // ----------------------------------------------------------------------------
 // Benchmark: Spread