Add support for Low Priorirty tasks.

Source/wtf/DoubleBufferedDequeTest.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "wtf/DoubleBufferedDeque.h"
 
 #include <gtest/gtest.h>
 
 namespace {
@@ skipping 32 matching lines @@
         EXPECT_EQ(100, deque.takeFirst());
     }
     queue.append(2);
 
     EXPECT_EQ(2, queue.swapBuffers().takeFirst());
     queue.append(3);
 
     EXPECT_EQ(3, queue.swapBuffers().takeFirst());
 }
 
+TEST(DoubleBufferedDequeTest, TestAllQueuesSize)
+{
+    DoubleBufferedDeque<int> queue;
+
+    EXPECT_EQ(0U, queue.allQueuesSize());
+
+    queue.append(10);
+    queue.append(20);
+    queue.append(30);
+
+    EXPECT_EQ(3U, queue.allQueuesSize());
+    queue.swapBuffers();
+
+    queue.append(10);
+    EXPECT_EQ(4U, queue.allQueuesSize());
+}
+
 } // namespace