Reland http://codereview.chromium.org/4139008, with a different

base/time_mac.cc

 // Copyright (c) 2008 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/time.h"
 
 #include <CoreFoundation/CFDate.h>
 #include <CoreFoundation/CFTimeZone.h>
 #include <mach/mach_time.h>
 #include <sys/time.h>
@@ skipping 44 matching lines @@
 
 // static
 Time Time::NowFromSystemTime() {
   // Just use Now() because Now() returns the system time.
   return Now();
 }
 
 // static
 Time Time::FromExploded(bool is_local, const Exploded& exploded) {
   CFGregorianDate date;
-  date.second = exploded.second +
-      exploded.millisecond / static_cast<double>(kMillisecondsPerSecond);
+  date.second = exploded.second;
   date.minute = exploded.minute;
   date.hour = exploded.hour;
   date.day = exploded.day_of_month;
   date.month = exploded.month;
   date.year = exploded.year;
 
   base::mac::ScopedCFTypeRef<CFTimeZoneRef>
       time_zone(is_local ? CFTimeZoneCopySystem() : NULL);
   CFAbsoluteTime seconds = CFGregorianDateGetAbsoluteTime(date, time_zone) +
       kCFAbsoluteTimeIntervalSince1970;
-  return Time(static_cast<int64>(seconds * kMicrosecondsPerSecond) +
+  Time result(static_cast<int64>(seconds * kMicrosecondsPerSecond) +
       kWindowsEpochDeltaMicroseconds);
+
+  // Need to add milliseconds in at the end because
+  // CFGregorianDateGetAbsoluteTime deals only in second resolution.
+  result += TimeDelta::FromMilliseconds(exploded.millisecond);
+  return result;
 }
 
 void Time::Explode(bool is_local, Exploded* exploded) const {
-  CFAbsoluteTime seconds =
+  double seconds =
       (static_cast<double>((us_ - kWindowsEpochDeltaMicroseconds) /
       kMicrosecondsPerSecond) - kCFAbsoluteTimeIntervalSince1970);
 
   base::mac::ScopedCFTypeRef<CFTimeZoneRef>
       time_zone(is_local ? CFTimeZoneCopySystem() : NULL);
-  CFGregorianDate date = CFAbsoluteTimeGetGregorianDate(seconds, time_zone);
+  CFGregorianDate date = CFAbsoluteTimeGetGregorianDate(
+      static_cast<CFAbsoluteTime>(seconds), time_zone);
 
   exploded->year = date.year;
   exploded->month = date.month;
   exploded->day_of_month = date.day;
   exploded->hour = date.hour;
   exploded->minute = date.minute;
   exploded->second = date.second;
-  exploded->millisecond  =
-      static_cast<int>(date.second * kMillisecondsPerSecond) %
-      kMillisecondsPerSecond;
+  exploded->millisecond = static_cast<int>(
+      static_cast<int64>(seconds * kMillisecondsPerSecond) % kMillisecondsPerSecond);
 }
 
 // TimeTicks ------------------------------------------------------------------
 
 // static
 TimeTicks TimeTicks::Now() {
   uint64_t absolute_micro;
 
   static mach_timebase_info_data_t timebase_info;
   if (timebase_info.denom == 0) {
@@ skipping 21 matching lines @@
 
   return TimeTicks(absolute_micro);
 }
 
 // static
 TimeTicks TimeTicks::HighResNow() {
   return Now();
 }
 
 }  // namespace base