Allow calling stats API functions before we have an isolate.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 0a7da7d74015c952ef71380634d93dd4aa1d17b0..af8054f1b446dd86ef7e6f92335427235cfb5820 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -4398,19 +4398,19 @@ void V8::SetCaptureStackTraceForUncaughtExceptions(
 
 
 void V8::SetCounterFunction(CounterLookupCallback callback) {
-  i::Isolate* isolate = i::Isolate::Current();
+  i::Isolate* isolate = EnterIsolateIfNeeded();
   if (IsDeadCheck(isolate, "v8::V8::SetCounterFunction()")) return;
   isolate->stats_table()->SetCounterFunction(callback);
 }
 
 void V8::SetCreateHistogramFunction(CreateHistogramCallback callback) {
-  i::Isolate* isolate = i::Isolate::Current();
+  i::Isolate* isolate = EnterIsolateIfNeeded();
   if (IsDeadCheck(isolate, "v8::V8::SetCreateHistogramFunction()")) return;
   isolate->stats_table()->SetCreateHistogramFunction(callback);
 }
 
 void V8::SetAddHistogramSampleFunction(AddHistogramSampleCallback callback) {
-  i::Isolate* isolate = i::Isolate::Current();
+  i::Isolate* isolate = EnterIsolateIfNeeded();
   if (IsDeadCheck(isolate, "v8::V8::SetAddHistogramSampleFunction()")) return;
   isolate->stats_table()->
       SetAddHistogramSampleFunction(callback);