Remove FilePathWatcher::PlatformDelegate::CancelOnMessageLoopThread().

base/files/file_path_watcher_mac.cc

Index: base/files/file_path_watcher_mac.cc
diff --git a/base/files/file_path_watcher_mac.cc b/base/files/file_path_watcher_mac.cc
index 7338eafa44408925314651a121c5f004ee373c21..b65591a22c97898745f8dfc2f3f369dc5b8dfa43 100644
--- a/base/files/file_path_watcher_mac.cc
+++ b/base/files/file_path_watcher_mac.cc
@@ -40,12 +40,6 @@ class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate {
     set_cancelled();
   }
 
-  void CancelOnMessageLoopThread() override {
-    if (impl_.get())
-      impl_->Cancel();
-    set_cancelled();
-  }
-
  protected:
   ~FilePathWatcherImpl() override {}