Fix Time::FromDoubleT so that it will return null time when 0 is passed.

This is the rework of this issue before previous submit is reverted. We need to
fix the usage of Time::FromDoubleT(0) in extension history API.

BUG=none
TEST=non

Review URL: http://codereview.chromium.org/3295001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@58953 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 15 insertions, 0 deletions

diff --git a/base/time.cc b/base/time.cc
index 383f939..766f599 100644
--- a/base/time.cc
+++ b/base/time.cc
@@ -66,6 +66,8 @@ time_t Time::ToTimeT() const {
 
 // static
 Time Time::FromDoubleT(double dt) {
+  if (dt == 0)
+    return Time();  // Preserve 0 so we can tell it doesn't exist.
   return Time(static_cast<int64>((dt *
                                   static_cast<double>(kMicrosecondsPerSecond)) +
                                  kTimeTToMicrosecondsOffset));
@@ -78,6 +80,13 @@ double Time::ToDoubleT() const {
           static_cast<double>(kMicrosecondsPerSecond));
 }
 
+// static
+Time Time::UnixEpoch() {
+  Time time;
+  time.us_ = kTimeTToMicrosecondsOffset;
+  return time;
+}
+
 Time Time::LocalMidnight() const {
   Exploded exploded;
   LocalExplode(&exploded);
diff --git a/base/time.h b/base/time.h
index 0f5eb5d..0ed7957 100644
--- a/base/time.h
+++ b/base/time.h
@@ -230,6 +230,9 @@ class Time {
     return us_ == 0;
   }
 
+  // Returns the time for epoch in Unix-like system (Jan 1, 1970).
+  static Time UnixEpoch();
+
   // Returns the current time. Watch out, the system might adjust its clock
   // in which case time will actually go backwards. We don't guarantee that
   // times are increasing, or that two calls to Now() won't be the same.
@@ -249,6 +252,9 @@ class Time {
 
   // Converts time to/from a double which is the number of seconds since epoch
   // (Jan 1, 1970).  Webkit uses this format to represent time.
+  // Because WebKit initializes double time value to 0 to indicate "not
+  // initialized", we map it to empty Time object that also means "not
+  // initialized".
   static Time FromDoubleT(double dt);
   double ToDoubleT() const;