Fix build by removing unused class member.

runtime/bin/eventhandler_linux.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef BIN_EVENTHANDLER_LINUX_H_
 #define BIN_EVENTHANDLER_LINUX_H_
 
 #if !defined(BIN_EVENTHANDLER_H_)
 #error Do not include eventhandler_linux.h directly; use eventhandler.h instead.
 #endif
@@ skipping 45 matching lines @@
 
   intptr_t fd() { return fd_; }
   Dart_Port port() { return port_; }
   bool tracked_by_epoll() { return tracked_by_epoll_; }
   void set_tracked_by_epoll(bool value) { tracked_by_epoll_ = value; }
 
  private:
   bool tracked_by_epoll_;
   intptr_t fd_;
   Dart_Port port_;
-  intptr_t mask_;
 };
 
 
 class EventHandlerImplementation {
  public:
   EventHandlerImplementation();
   ~EventHandlerImplementation();
 
   // Gets the socket data structure for a given file
   // descriptor. Creates a new one if one is not found.
@@ skipping 17 matching lines @@
   bool shutdown_;
   int interrupt_fds_[2];
   int epoll_fd_;
   int timer_fd_;
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_EVENTHANDLER_LINUX_H_