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 de9d0750ce6f68df6cd0ad95b67edfd4299aab18..7e3a9d2e439c03fa3d9121b3cf9ab92101d171fc 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -7648,13 +7648,13 @@ 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();
 }