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

runtime/bin/file_macos.cc

Index: runtime/bin/file_macos.cc
diff --git a/runtime/bin/file_macos.cc b/runtime/bin/file_macos.cc
index 67869e3124591f27a0d97f9bbd5dbf7b9177552d..301424b3daface22b3ad7cb6927934d3308de97c 100644
--- a/runtime/bin/file_macos.cc
+++ b/runtime/bin/file_macos.cc
@@ -296,4 +296,18 @@ File::Type File::GetType(const char* pathname, bool follow_links) {
   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)