VM eventhandler: Read "old" event mask before it can be modified.

runtime/bin/eventhandler_macos.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 RUNTIME_BIN_EVENTHANDLER_MACOS_H_
 #define RUNTIME_BIN_EVENTHANDLER_MACOS_H_
 
 #if !defined(RUNTIME_BIN_EVENTHANDLER_H_)
 #error Do not include eventhandler_macos.h directly; use eventhandler.h instead.
 #endif
 
 #include <errno.h>
 #include <sys/event.h>  // NOLINT
 #include <sys/socket.h>
 #include <unistd.h>
 
 #include "platform/hashmap.h"
 #include "platform/signal_blocker.h"
 
 
 namespace dart {
 namespace bin {
 
 class DescriptorInfo : public DescriptorInfoBase {
  public:
-  explicit DescriptorInfo(intptr_t fd)
-      : DescriptorInfoBase(fd), tracked_by_kqueue_(false) {}
+  explicit DescriptorInfo(intptr_t fd) : DescriptorInfoBase(fd) {}
 
   virtual ~DescriptorInfo() {}
 
   intptr_t GetPollEvents();
 
   virtual void Close() {
     VOID_TEMP_FAILURE_RETRY(close(fd_));
     fd_ = -1;
   }
 
-  void set_tracked_by_kqueue(bool value) { tracked_by_kqueue_ = value; }
-
-  bool tracked_by_kqueue() { return tracked_by_kqueue_; }
-
   bool HasReadEvent();
 
   bool HasWriteEvent();
 
- protected:
-  bool tracked_by_kqueue_;
-
  private:
   DISALLOW_COPY_AND_ASSIGN(DescriptorInfo);
 };
 
 
 class DescriptorInfoSingle : public DescriptorInfoSingleMixin<DescriptorInfo> {
  public:
   explicit DescriptorInfoSingle(intptr_t fd)
       : DescriptorInfoSingleMixin(fd, false) {}
   virtual ~DescriptorInfoSingle() {}
@@ skipping 47 matching lines @@
   int interrupt_fds_[2];
   int kqueue_fd_;
 
   DISALLOW_COPY_AND_ASSIGN(EventHandlerImplementation);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // RUNTIME_BIN_EVENTHANDLER_MACOS_H_