Fix debuggersupport=off build after r17184 and r18149.

src/d8-debug.h

 // Copyright 2008 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 13 matching lines @@
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #ifndef V8_D8_DEBUG_H_
 #define V8_D8_DEBUG_H_
 
 
 #include "d8.h"
 #include "debug.h"
+#include "platform/socket.h"
 
 
 namespace v8 {
 
 
 void HandleDebugEvent(const Debug::EventDetails& event_details);
 
 // Start the remove debugger connecting to a V8 debugger agent on the specified
 // port.
 void RunRemoteDebugger(Isolate* isolate, int port);
@@ skipping 102 matching lines @@
   RemoteDebuggerEvent* next_;
 
   friend class RemoteDebugger;
 };
 
 
 }  // namespace v8
 
 
 #endif  // V8_D8_DEBUG_H_