Fix idle ticks during isolate startup

runtime/vm/thread.cc

Index: runtime/vm/thread.cc
diff --git a/runtime/vm/thread.cc b/runtime/vm/thread.cc
index 214007808a903c1b2c49aff99c95434e0c1332d2..573c11b3ca23d8f658648d8708a989a4f4fb8064 100644
--- a/runtime/vm/thread.cc
+++ b/runtime/vm/thread.cc
@@ -77,7 +77,11 @@ void Thread::ExitIsolate() {
   if (thread == NULL) return;
   Isolate* isolate = thread->isolate();
   ASSERT(isolate != NULL);
-  isolate->set_vm_tag(VMTag::kIdleTagId);
+  if (isolate->is_runnable()) {
+    isolate->set_vm_tag(VMTag::kIdleTagId);
+  } else {
+    isolate->set_vm_tag(VMTag::kLoadWaitTagId);
+  }
   isolate->set_thread_state(NULL);
   Profiler::EndExecution(isolate);
   isolate->set_mutator_thread(NULL);