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

src/profile-generator.cc

Index: src/profile-generator.cc
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index 86bd17b70a08b304dd40af5424127a3659436714..838b682663a464c3667048d80458f3245bb4d947 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -376,8 +376,8 @@ CpuProfile::CpuProfile(const char* title, unsigned uid, bool record_samples)
     : title_(title),
       uid_(uid),
       record_samples_(record_samples),
-      start_time_us_(OS::Ticks()),
-      end_time_us_(0) {
+      start_time_(Time::NowFromSystemTime()) {
+  timer_.Start();
 }
 
 
@@ -388,10 +388,11 @@ void CpuProfile::AddPath(const Vector<CodeEntry*>& path) {
 
 
 void CpuProfile::CalculateTotalTicksAndSamplingRate() {
-  end_time_us_ = OS::Ticks();
+  TimeDelta duration = timer_.Elapsed();
+  end_time_ = start_time_ + duration;
   top_down_.CalculateTotalTicks();
 
-  double duration_ms = (end_time_us_ - start_time_us_) / 1000.;
+  double duration_ms = duration.InMillisecondsF();
   if (duration_ms < 1) duration_ms = 1;
   unsigned ticks = top_down_.root()->total_ticks();
   double rate = ticks / duration_ms;