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

src/platform-nullos.cc

Index: src/platform-nullos.cc
diff --git a/src/platform-nullos.cc b/src/platform-nullos.cc
index dc7adb6b47ec5b765fb961c57024267c2e2bfd2b..b79fa881a13b6a5a4e8db5df217eb31fae7a2458 100644
--- a/src/platform-nullos.cc
+++ b/src/platform-nullos.cc
@@ -113,13 +113,6 @@ double OS::TimeCurrentMillis() {
 }
 
 
-// Returns ticks in microsecond resolution.
-int64_t OS::Ticks() {
-  UNIMPLEMENTED();
-  return 0;
-}
-
-
 // Returns a string identifying the current timezone taking into
 // account daylight saving.
 const char* OS::LocalTimezone(double time) {