Remove tcmalloc when not being used. Restore shim on Windows.

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"
 
-#include "base/logging.h"
+#include "base/basictypes.h"
 
 namespace {
 
 tracked_objects::NowFunction* g_time_function = NULL;
 tracked_objects::TimeSourceType g_time_source_type =
     tracked_objects::TIME_SOURCE_TYPE_WALL_TIME;
 
 }  // anonymous namespace
 
 namespace tracked_objects {
 
 const char kAlternateProfilerTime[] = "CHROME_PROFILER_TIME";
 
 // Set an alternate timer function to replace the OS time function when
 // profiling.
 void SetAlternateTimeSource(NowFunction* now_function, TimeSourceType type) {
-  DCHECK_EQ(reinterpret_cast<NowFunction*>(NULL), g_time_function);
   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