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

src/platform-openbsd.cc

Index: src/platform-openbsd.cc
diff --git a/src/platform-openbsd.cc b/src/platform-openbsd.cc
index e59160109f0fbfc7c6ab0b6fd6b088ae0bc3dd1f..a027944145f67d493445689505be540e5771a302 100644
--- a/src/platform-openbsd.cc
+++ b/src/platform-openbsd.cc
@@ -500,7 +500,7 @@ Semaphore* OS::CreateSemaphore(int count) {
 
 void OS::SetUp() {
   // Seed the random number generator. We preserve microsecond resolution.
-  uint64_t seed = Ticks() ^ (getpid() << 16);
+  uint64_t seed = static_cast<uint64_t>(TimeCurrentMillis()) ^ (getpid() << 16);
   srandom(static_cast<unsigned int>(seed));
   limit_mutex = CreateMutex();
 }