diff --git a/src/tests/markidle_unittest.cc b/src/tests/markidle_unittest.cc
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+++ b/src/tests/markidle_unittest.cc
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+// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
+// Copyright (c) 2003, Google Inc.
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+// 
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// ---
+// Author: Sanjay Ghemawat
+//
+// MallocExtension::MarkThreadIdle() testing
+#include <stdio.h>
+
+#include "config_for_unittests.h"
+#include "base/logging.h"
+#include <gperftools/malloc_extension.h>
+#include "tests/testutil.h"   // for RunThread()
+
+// Helper routine to do lots of allocations
+static void TestAllocation() {
+  static const int kNum = 100;
+  void* ptr[kNum];
+  for (int size = 8; size <= 65536; size*=2) {
+    for (int i = 0; i < kNum; i++) {
+      ptr[i] = malloc(size);
+    }
+    for (int i = 0; i < kNum; i++) {
+      free(ptr[i]);
+    }
+  }
+}
+
+// Routine that does a bunch of MarkThreadIdle() calls in sequence
+// without any intervening allocations
+static void MultipleIdleCalls() {
+  for (int i = 0; i < 4; i++) {
+    MallocExtension::instance()->MarkThreadIdle();
+  }
+}
+
+// Routine that does a bunch of MarkThreadIdle() calls in sequence
+// with intervening allocations
+static void MultipleIdleNonIdlePhases() {
+  for (int i = 0; i < 4; i++) {
+    TestAllocation();
+    MallocExtension::instance()->MarkThreadIdle();
+  }
+}
+
+// Get current thread cache usage
+static size_t GetTotalThreadCacheSize() {
+  size_t result;
+  CHECK(MallocExtension::instance()->GetNumericProperty(
+            "tcmalloc.current_total_thread_cache_bytes",
+            &result));
+  return result;
+}
+
+// Check that MarkThreadIdle() actually reduces the amount
+// of per-thread memory.
+static void TestIdleUsage() {
+  const size_t original = GetTotalThreadCacheSize();
+
+  TestAllocation();
+  const size_t post_allocation = GetTotalThreadCacheSize();
+  CHECK_GT(post_allocation, original);
+
+  MallocExtension::instance()->MarkThreadIdle();
+  const size_t post_idle = GetTotalThreadCacheSize();
+  CHECK_LE(post_idle, original);
+
+  // Log after testing because logging can allocate heap memory.
+  VLOG(0, "Original usage: %" PRIuS "\n", original);
+  VLOG(0, "Post allocation: %" PRIuS "\n", post_allocation);
+  VLOG(0, "Post idle: %" PRIuS "\n", post_idle);
+}
+
+int main(int argc, char** argv) {
+  RunThread(&TestIdleUsage);
+  RunThread(&TestAllocation);
+  RunThread(&MultipleIdleCalls);
+  RunThread(&MultipleIdleNonIdlePhases);
+
+  printf("PASS\n");
+  return 0;
+}