Always initialize the debugger eagerly.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index fdd89b4f4e605fc06834200079e343c4bb96d695..f1cfab0e1703d7e888012050ed32b738910c6709 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -928,14 +928,8 @@ class Isolate {
 
   inline bool IsCodePreAgingActive();
 
-  Debugger* debugger() {
-    if (!NoBarrier_Load(&debugger_initialized_)) InitializeDebugger();
-    return debugger_;
-  }
-  Debug* debug() {
-    if (!NoBarrier_Load(&debugger_initialized_)) InitializeDebugger();
-    return debug_;
-  }
+  Debugger* debugger() {  return debugger_; }
+  Debug* debug() { return debug_; }
 
   inline bool IsDebuggerActive();
   inline bool DebuggerHasBreakPoints();
@@ -1180,8 +1174,6 @@ class Isolate {
 
   void PropagatePendingExceptionToExternalTryCatch();
 
-  void InitializeDebugger();
-
   // Traverse prototype chain to find out whether the object is derived from
   // the Error object.
   bool IsErrorObject(Handle<Object> obj);