Enable asynchronous remote debugging with d8.

src/d8-readline.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 73 matching lines @@
   return read_history(kHistoryFileName) == 0;
 }
 
 
 bool ReadLineEditor::Close() {
   return write_history(kHistoryFileName) == 0;
 }
 
 
 Handle<String> ReadLineEditor::Prompt(const char* prompt) {
-  char* result = readline(prompt);
+  char* result = NULL;
+  {  // Release lock for blocking input.
+    Unlocker unlock(Isolate::GetCurrent());
+    result = readline(prompt);
+  }
   if (result != NULL) {
     AddHistory(result);
   } else {
     return Handle<String>();
   }
   return String::New(result);
 }
 
 
 void ReadLineEditor::AddHistory(const char* str) {
@@ skipping 42 matching lines @@
     return strdup(*str);
   } else {
     current_completions.Dispose();
     current_completions.Clear();
     return NULL;
   }
 }
 
 
 }  // namespace v8