[d8 Workers] Add max worker count, throw an exception if too many.

test/mjsunit/regress/regress-crbug-518748.js

Index: test/mjsunit/regress/regress-crbug-518748.js
diff --git a/test/mjsunit/regress/regress-crbug-503698.js b/test/mjsunit/regress/regress-crbug-518748.js
similarity index 56%
copy from test/mjsunit/regress/regress-crbug-503698.js
copy to test/mjsunit/regress/regress-crbug-518748.js
index 415d1bc81be5ac46fb358ce8ec681b1e5c276e07..bbbf4d60197821e4b95a47f886b2e3861ccf4484 100644
--- a/test/mjsunit/regress/regress-crbug-503698.js
+++ b/test/mjsunit/regress/regress-crbug-518748.js
@@ -2,8 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --invoke-weak-callbacks
-
 if (this.Worker) {
-  var __v_6 = new Worker('');
+  function f(a) {
+    assertThrows(function() {
+      for (var i = 0; new Worker('onmessage = function() {};'); i++) a[i] = i;

[Michael Starzinger, 2015/08/10 22:01:23]

The regression test is kind of brittle, because if the workers finish fast
enough, there will never be more than 100 of them running in parallel. We need
some more reliable way to test that. Also a loop that doesn't run infinitely but
is bounded somehow would be better.

[binji, 2015/08/10 22:09:47]

Workers are not reaped until the main thread is finished, so this should not be
a problem. But if someone decided to fix that, you're right. In any case, there
needs to be a better test because this is failing on multiple bots as-is. :)

[Michael Starzinger, 2015/08/10 22:14:41]

Ah, got it. My bad, I was assuming the {workers} list in d8.cc would be emptied
out whenever a worker terminated. But yes, as you mentioned, for some reason
some try-bots still fail on this test, so it's brittle for other reasons.

+    });
+  }
+  f([]);
 }