Reland #1: "base: Implement GetCurrentThreadPriority."

components/startup_metric_utils/browser/startup_metric_utils.cc

 // Copyright 2013 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 "components/startup_metric_utils/browser/startup_metric_utils.h"
 
 #include <stddef.h>
 
 #include <memory>
 
@@ skipping 298 matching lines @@
 // also the time taken to synchronously resolve base::Time::Now() and
 // base::TimeTicks::Now() at play, but in practice it is pretty much instant
 // compared to multi-seconds startup timings.
 base::TimeTicks StartupTimeToTimeTicks(const base::Time& time) {
   // First get a base which represents the same point in time in both units.
   // Bump the priority of this thread while doing this as the wall clock time it
   // takes to resolve these two calls affects the precision of this method and
   // bumping the priority reduces the likelihood of a context switch interfering
   // with this computation.
 
-// Enabling this logic on OS X causes a significant performance regression.
-// https://crbug.com/601270
-#if !defined(OS_MACOSX)
   static bool statics_initialized = false;
 
   base::ThreadPriority previous_priority = base::ThreadPriority::NORMAL;
   if (!statics_initialized) {
     previous_priority = base::PlatformThread::GetCurrentThreadPriority();
     base::PlatformThread::SetCurrentThreadPriority(
         base::ThreadPriority::DISPLAY);
   }
-#endif
 
   static const base::Time time_base = base::Time::Now();
   static const base::TimeTicks trace_ticks_base = base::TimeTicks::Now();
 
-#if !defined(OS_MACOSX)
   if (!statics_initialized) {
     base::PlatformThread::SetCurrentThreadPriority(previous_priority);
   }
   statics_initialized = true;
-#endif
 
   // Then use the TimeDelta common ground between the two units to make the
   // conversion.
   const base::TimeDelta delta_since_base = time_base - time;
   return trace_ticks_base - delta_since_base;
 }
 
 // Record time of main entry so it can be read from Telemetry performance tests.
 // TODO(jeremy): Remove once crbug.com/317481 is fixed.
 void RecordMainEntryTimeHistogram() {
@@ skipping 396 matching lines @@
 
 base::TimeTicks MainEntryPointTicks() {
   return g_browser_main_entry_point_ticks.Get();
 }
 
 StartupTemperature GetStartupTemperature() {
   return g_startup_temperature;
 }
 
 }  // namespace startup_metric_utils