SequenceBound: migrate from Post() to AsyncCall() in //components/services/filesystem.

Bug: 1140588
Change-Id: I6df170a66838d46babbcbf44d48c43dcfbe7e9ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2488420Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819480}

components/services/filesystem/directory_test_helper.cc

@@ -52,8 +52,8 @@ DirectoryTestHelper::~DirectoryTestHelper() = default;
 
 mojo::Remote<mojom::Directory> DirectoryTestHelper::CreateTempDir() {
   mojo::Remote<mojom::Directory> remote;
-  blocking_state_.Post(FROM_HERE, &BlockingState::BindNewTempDirectory,
-                       remote.BindNewPipeAndPassReceiver());
+  blocking_state_.AsyncCall(&BlockingState::BindNewTempDirectory)
+      .WithArgs(remote.BindNewPipeAndPassReceiver());
   return remote;
 }