new benchmark for SizedQueue

The performance of SizedQueue is a bit more complex than
regular Queue, so it deserves a separate benchmark.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58509 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

benchmark/bm_vm_thread_sized_queue.rb

@@ -0,0 +1,19 @@
+require 'thread'
+
+n = 1_000_000
+q = Thread::SizedQueue.new(100)
+consumer = Thread.new{
+  while q.pop
+    # consuming
+  end
+}
+
+producer = Thread.new{
+  while n > 0
+    q.push true
+    n -= 1
+  end
+  q.push nil
+}
+
+consumer.join