Support use of third party time function to profiler

base/profiler/alternate_timer.h

+// 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.
+
+// This is a glue file, which allows third party code to call into our profiler
+// without having to include most any functions from base.
+
+
+#ifndef BASE_PROFILER_ALTERNATE_TIMER_H_
+#define BASE_PROFILER_ALTERNATE_TIMER_H_
+
+namespace tracked_objects {
+
+// Provide type for an alternate timer function.
+typedef unsigned int NowFunction();
+
+// Set an alternate timer function to replace the OS time function when
+// profiling.  Typically this is called by an allocator that is providing a
+// function that indicates how much memory has been allocated on any given
+// thread.
+extern void SetAlternateTimeSource(NowFunction* now_function);
+
+// Gets the pointer to a function that was set via SetAlternateTimeSource().
+// Returns NULL if no set was done prior to calling GetAlternateTimeSource.
+extern NowFunction* GetAlternateTimeSource();
+
+// Environment variable name that is used to activate alternate timer profiling
+// (such as using TCMalloc allocations to provide a pseudo-timer) for tasks
+// instead of wall clock profiling.
+extern const char kAlternateProfilerTime[];
+
+
+
+}  // tracked_objects
+
+#endif  // BASE_PROFILER_ALTERNATE_TIMER_H_