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 b1dadc1a180eccabfeca47da1b68cca5a7677454..def0097464d8b088f533724ba2ffd24c9e8adcc5 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -334,8 +334,8 @@ 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();
 }
 
 
@@ -346,7 +346,7 @@ void CpuProfile::AddPath(const Vector<CodeEntry*>& path) {
 
 
 void CpuProfile::CalculateTotalTicksAndSamplingRate() {
-  end_time_us_ = OS::Ticks();
+  end_time_ = start_time_ + timer_.Elapsed();
 }