Add Chromium-style TimeDelta, Time and TimeTicks classes, and a new ElapsedTimer class.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 704ec8d5ec18bab197aa602077b63867d8b1dd85..904aec3bd15bff842e0ab9d25e064ebff4178809 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -7391,13 +7391,13 @@ const CpuProfileNode* CpuProfile::GetSample(int index) const {
 
 int64_t CpuProfile::GetStartTime() const {
   const i::CpuProfile* profile = reinterpret_cast<const i::CpuProfile*>(this);
-  return profile->start_time_us();
+  return (profile->start_time() - i::Time::UnixEpoch()).InMicroseconds();
 }
 
 
 int64_t CpuProfile::GetEndTime() const {
   const i::CpuProfile* profile = reinterpret_cast<const i::CpuProfile*>(this);
-  return profile->end_time_us();
+  return (profile->end_time() - i::Time::UnixEpoch()).InMicroseconds();
 }