Move vm_tags from isolate to thread, since we may have multiple threads in same isolate (GC, backgr…

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 669af56660e4a18d15d85ef8cc23709f8b20a95c..df55fd14f6b28186c4dc1bc500a69bac3dac420a 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -768,7 +768,7 @@ Isolate::Isolate(const Dart_IsolateFlags& api_flags)
       REUSABLE_HANDLE_LIST(REUSABLE_HANDLE_SCOPE_INIT)
       reusable_handles_() {
   flags_.CopyFrom(api_flags);
-  set_vm_tag(VMTag::kEmbedderTagId);
+  Thread::Current()->set_vm_tag(VMTag::kEmbedderTagId);
   set_user_tag(UserTags::kDefaultUserTag);
 }
 
@@ -1937,7 +1937,8 @@ intptr_t Isolate::ProfileInterrupt() {
 
 
 void Isolate::ProfileIdle() {
-  vm_tag_counters_.Increment(vm_tag());
+  // Currently we are only sampling the mutator thread.
+  vm_tag_counters_.Increment(VMTag::kIdleTagId);
 }