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

base/time_mac.cc

Index: base/time_mac.cc
diff --git a/base/time_mac.cc b/base/time_mac.cc
index 6dfaa20e00fdc964bac80e6f915671b924b5b89b..e9781a611f8cfd7fa41767a6a5782e07a65c22ff 100644
--- a/base/time_mac.cc
+++ b/base/time_mac.cc
@@ -62,8 +62,7 @@ Time Time::NowFromSystemTime() {
 // 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;
@@ -74,18 +73,24 @@ Time Time::FromExploded(bool is_local, const Exploded& exploded) {
       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;
@@ -93,9 +98,8 @@ void Time::Explode(bool is_local, Exploded* exploded) const {
   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 ------------------------------------------------------------------