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

runtime/bin/eventhandler_macos.h

Index: runtime/bin/eventhandler_macos.h
diff --git a/runtime/bin/eventhandler_macos.h b/runtime/bin/eventhandler_macos.h
index 414dfbef2771c0d7cce81796117ee310bda871ca..e6a5f939b505ac5aabbcc5756aee627df5142a72 100644
--- a/runtime/bin/eventhandler_macos.h
+++ b/runtime/bin/eventhandler_macos.h
@@ -23,8 +23,7 @@ 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() {}
 
@@ -35,17 +34,10 @@ class DescriptorInfo : public DescriptorInfoBase {
     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);
 };