Don't create debug context if debug listener is not set

include/v8-debug.h

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_V8_DEBUG_H_
 #define V8_V8_DEBUG_H_
 
 #include "v8.h"
 
 /**
@@ skipping 230 matching lines @@
    *
    * "Evaluate" debug command behavior currently is not specified in scope
    * of this method.
    */
   static void ProcessDebugMessages();
 
   /**
    * Debugger is running in its own context which is entered while debugger
    * messages are being dispatched. This is an explicit getter for this
    * debugger context. Note that the content of the debugger context is subject
-   * to change.
+   * to change. The Context exists only when the debugger is active, i.e. at
+   * least one DebugEventListener or MessageHandler is set.
    */
   static Local<Context> GetDebugContext();
 
 
   /**
    * Enable/disable LiveEdit functionality for the given Isolate
    * (default Isolate if not provided). V8 will abort if LiveEdit is
    * unexpectedly used. LiveEdit is enabled by default.
    */
   static void SetLiveEditEnabled(Isolate* isolate, bool enable);
 };
 
 
 }  // namespace v8
 
 
 #undef EXPORT
 
 
 #endif  // V8_V8_DEBUG_H_