Preparation for moving reusable handles to thread and more cleanups: isolate -> thread based handle…

runtime/vm/debugger.h

Index: runtime/vm/debugger.h
diff --git a/runtime/vm/debugger.h b/runtime/vm/debugger.h
index 7c4cb8a3436a79452b680be789b8741a9e4eb923..c182065dfd929ed3937cac29df36c3dd9ebffab7 100644
--- a/runtime/vm/debugger.h
+++ b/runtime/vm/debugger.h
@@ -453,7 +453,7 @@ class Debugger {
   Debugger();
   ~Debugger();
 
-  void Initialize(Isolate* isolate);
+  void Initialize(Thread* thread);
   void NotifyIsolateCreated();
   void Shutdown();
 
@@ -650,6 +650,7 @@ class Debugger {
 
   void HandleSteppingRequest(DebuggerStackTrace* stack_trace);
 
+  Thread* thread_;
   Isolate* isolate_;
   Dart_Port isolate_id_;  // A unique ID for the isolate in the debugger.
   bool initialized_;