profiler: cleanup unused alternate_timer code

base/profiler/alternate_timer.cc

-// 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"
-
-namespace {
-
-tracked_objects::NowFunction* g_time_function = nullptr;
-tracked_objects::TimeSourceType g_time_source_type =
-    tracked_objects::TIME_SOURCE_TYPE_WALL_TIME;
-
-}  // anonymous namespace
-
-namespace tracked_objects {
-
-// Set an alternate timer function to replace the OS time function when
-// profiling.
-void SetAlternateTimeSource(NowFunction* now_function, TimeSourceType type) {
-  g_time_function = now_function;
-  g_time_source_type = type;
-}
-
-NowFunction* GetAlternateTimeSource() {
-  return g_time_function;
-}
-
-TimeSourceType GetTimeSourceType() {
-  return g_time_source_type;
-}
-
-}  // namespace tracked_objects