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

BUG=chromium:518748
R=mstarzinger@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/1284683004

Cr-Commit-Position: refs/heads/master@{#30230}

src/d8.cc

@@ -75,6 +75,7 @@ namespace v8 {
 namespace {
 
 const int MB = 1024 * 1024;
+const int kMaxWorkers = 50;
 
 
 class ShellArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
@@ -706,6 +707,11 @@ void Shell::WorkerNew(const v8::FunctionCallbackInfo<v8::Value>& args) {
 
   {
     base::LockGuard<base::Mutex> lock_guard(workers_mutex_.Pointer());
+    if (workers_.length() >= kMaxWorkers) {
+      Throw(args.GetIsolate(), "Too many workers, I won't let you create more");
+      return;
+    }
+
     // Initialize the internal field to NULL; if we return early without
     // creating a new Worker (because the main thread is terminating) we can
     // early-out from the instance calls.

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

+// Copyright 2015 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.
+
+if (this.Worker) {
+  var workersToCreate = 1000;
+  var workers = [];
+  assertThrows(function() {
+    for (var i = 0; i < workersToCreate; i++) {
+      workers.push(new Worker(''));
+    }
+  });
+  print('#workers: ', workers.length);
+}