[test] Fix flaky OOM regression test

The test was originally testing the max string length limit, but due to
refactoring of Array.join started consuming too much memory, resulting in
OOMs on TSAN builds. The new implementation still checks for the limit,
while reducing the memory consumption drastically.

R=jarin@chromium.org

Bug: v8:8504, chromium:336820
Change-Id: I4db9001541103d5908149e623ce4a4beee551e6c
Reviewed-on: https://chromium-review.googlesource.com/c/1426839Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59000}

test/mjsunit/regress/regress-336820.js

@@ -28,11 +28,10 @@
 // Flags: --max-old-space-size=1600
 
 assertThrows((function() {
-  s = "Hello World!\n";
-  while (true) {
-    x = new Array();
-    x[0] = s;
-    x[1000] = s;
-    x[10000] = s;
-    s = x.join("::");
-  }}), RangeError);
+  let str = "a".repeat(1e7);
+  let arr = new Array(2000);
+  for (let i = 0; i < 200; ++i) {
+    arr[i*10] = str;
+  }
+  let res = arr.join(':');
+}), RangeError);