Add FileSystemWatcher class to dart:io.

runtime/bin/eventhandler_win.h

Index: runtime/bin/eventhandler_win.h
diff --git a/runtime/bin/eventhandler_win.h b/runtime/bin/eventhandler_win.h
index 1c62200853866744b377565cd0488b8a72e5ab5a..1e7554c64c968c18b3b96308b13af3a335d2b416 100644
--- a/runtime/bin/eventhandler_win.h
+++ b/runtime/bin/eventhandler_win.h
@@ -130,7 +130,12 @@ class OverlappedBuffer {
 // sockets.
 class Handle {
  public:
-  enum Type { kFile, kClientSocket, kListenSocket };
+  enum Type {
+    kFile,
+    kDirectoryWatch,
+    kClientSocket,
+    kListenSocket
+  };
 
   class ScopedLock {
    public:
@@ -256,6 +261,27 @@ class FileHandle : public Handle {
 };
 
 
+class DirectoryWatchHandle : public Handle {
+ public:
+  DirectoryWatchHandle(HANDLE handle, int events, bool recursive)
+      : Handle(reinterpret_cast<HANDLE>(handle)),
+        events_(events),
+        recursive_(recursive) {
+    type_ = kDirectoryWatch;
+  }
+
+  virtual void EnsureInitialized(EventHandlerImplementation* event_handler);
+  virtual bool IsClosed();
+  virtual void DoClose();
+
+  virtual bool IssueRead();
+
+ private:
+  int events_;
+  bool recursive_;
+};
+
+
 class SocketHandle : public Handle {
  public:
   SOCKET socket() { return reinterpret_cast<SOCKET>(handle_); }