Support use of third party time function to profiler

base/profiler/alternate_timer.cc

Index: base/profiler/alternate_timer.cc
===================================================================
--- base/profiler/alternate_timer.cc	(revision 0)
+++ base/profiler/alternate_timer.cc	(revision 0)
@@ -0,0 +1,23 @@
+// Copyright (c) 2012 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 "base/profiler/alternate_timer.h"
+
+#include "base/logging.h"
+
+namespace tracked_objects {
+
+static NowFunction* g_time_function = NULL;
+
+// Set an alternate timer function to replace the OS time function when
+// profiling.
+void SetAlternateTimeSource(NowFunction* now_function) {
+  DCHECK_EQ(g_time_function, reinterpret_cast<NowFunction*>(NULL));
+  g_time_function = now_function;
+}
+
+extern NowFunction* GetAlternateTimeSource() {
+  return g_time_function;
+}
+}  // tracked_objects