Completely remove InterruptableThreadState and Fix ThreadRegistry leak

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 3d06d6f091662382d079c13919042702373feb7c..e5873ea3150eeb38280716c1b91fc364d9217835 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -634,10 +634,6 @@ class Isolate : public BaseIsolate {
 
   void PrintJSON(JSONStream* stream, bool ref = true);
 
-  InterruptableThreadState* thread_state() const {
-    return (mutator_thread_ == NULL) ? NULL : mutator_thread_->thread_state();
-  }
-
   CompilerStats* compiler_stats() {
     return compiler_stats_;
   }
@@ -917,7 +913,6 @@ class Isolate : public BaseIsolate {
   // Manage list of existing isolates.
   static void AddIsolateTolist(Isolate* isolate);
   static void RemoveIsolateFromList(Isolate* isolate);
-  static void CheckForDuplicateThreadState(InterruptableThreadState* state);
 
   static Monitor* isolates_list_monitor_;  // Protects isolates_list_head_
   static Isolate* isolates_list_head_;