Time isolate initialization.

This mirrors the way we time context initialization.

R=jgruber@chromium.org

Change-Id: I1bddc73726ef86e5863012c292e7b4c39dfd076f
Reviewed-on: https://chromium-review.googlesource.com/968241Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52009}

src/isolate.cc

@@ -2885,6 +2885,9 @@ void Isolate::PrepareEmbeddedBlobForSerialization() {
 bool Isolate::Init(StartupDeserializer* des) {
   TRACE_ISOLATE(init);
 
+  base::ElapsedTimer timer;
+  if (des == nullptr && FLAG_profile_deserialization) timer.Start();
+
   time_millis_at_init_ = heap_.MonotonicallyIncreasingTimeInMs();
 
   stress_deopt_count_ = FLAG_deopt_every_n_times;
@@ -3101,6 +3104,11 @@ bool Isolate::Init(StartupDeserializer* des) {
                                                sampling_flags);
   }
 
+  if (des == nullptr && FLAG_profile_deserialization) {
+    double ms = timer.Elapsed().InMillisecondsF();
+    PrintF("[Initializing isolate from scratch took %0.3f ms]\n", ms);
+  }
+
   return true;
 }