Switch CPU profile start/stop markers to monotonic time.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 3550bb04de9697ab9df06872172c6ffc91aa2c43..1530ff03f340a3206624d6ba99ee100a8fbe2002 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -7084,13 +7084,13 @@ 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() - i::Time::UnixEpoch()).InMicroseconds();
+  return (profile->start_time() - i::TimeTicks()).InMicroseconds();
 }
 
 
 int64_t CpuProfile::GetEndTime() const {
   const i::CpuProfile* profile = reinterpret_cast<const i::CpuProfile*>(this);
-  return (profile->end_time() - i::Time::UnixEpoch()).InMicroseconds();
+  return (profile->end_time() - i::TimeTicks()).InMicroseconds();
 }