Implement File.directory() and File.directorySync() to get

runtime/bin/file_macos.cc

 // 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.
 
 #include "bin/file.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ skipping 166 matching lines @@
     ASSERT(resolved_path != NULL);
     do {
       abs_path = realpath(pathname, NULL);
     } while (abs_path == NULL && errno == EINTR);
     ASSERT(abs_path == NULL || IsAbsolutePath(abs_path));
   }
   return abs_path;
 }
 
 
+char* File::GetContainingDirectory(char* pathname) {
+  ASSERT(Exists(pathname));
+  char* path = NULL;
+  do {
+    path = dirname(pathname);
+  } while (path == NULL && errno == EINTR);
+  return GetCanonicalPath(path);
+}
+
+
 const char* File::PathSeparator() {
   return "/";
 }
 
 
 const char* File::StringEscapedPathSeparator() {
   return "/";
 }
 
 
 File::StdioHandleType File::GetStdioHandleType(int fd) {
   ASSERT(0 <= fd && fd <= 2);
   struct stat buf;
   int result = fstat(fd, &buf);
   if (result == -1) {
     FATAL2("Failed stat on file descriptor %d: %s", fd, strerror(errno));
   }
   if (S_ISCHR(buf.st_mode)) return kTerminal;
   if (S_ISFIFO(buf.st_mode)) return kPipe;
   if (S_ISREG(buf.st_mode)) return kFile;
   return kOther;
 }