Add FileSystemEntity.identical, to test if two file system objects are the same.

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 "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "bin/file.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 278 matching lines @@
   } else {
     stat_success = TEMP_FAILURE_RETRY(lstat(pathname, &entry_info));
   }
   if (stat_success == -1) return File::kDoesNotExist;
   if (S_ISDIR(entry_info.st_mode)) return File::kIsDirectory;
   if (S_ISREG(entry_info.st_mode)) return File::kIsFile;
   if (S_ISLNK(entry_info.st_mode)) return File::kIsLink;
   return File::kDoesNotExist;
 }
 
+
+File::Identical File::AreIdentical(const char* file_1, const char* file_2) {
+  struct stat file_1_info;
+  struct stat file_2_info;
+  if (TEMP_FAILURE_RETRY(lstat(file_1, &file_1_info)) == -1 ||
+      TEMP_FAILURE_RETRY(lstat(file_2, &file_2_info)) == -1) {
+    return File::kError;
+  }
+  return (file_1_info.st_ino == file_2_info.st_ino &&
+          file_1_info.st_dev == file_2_info.st_dev) ?
+      File::kIdentical :
+      File::kDifferent;
+}
+
 #endif  // defined(TARGET_OS_MACOS)