docs: private void enqueueDiskWrite(final MemoryCommitResult mcr,
                                    final Runnable postWriteRunnable) {
          final Runnable writeToDiskRunnable = new Runnable() {
              public void run() {
                  synchronized (mWritingToDiskLock) {
                      writeToFile(mcr);
                  }
                  synchronized (XmlStorage.this) {
                      mDiskWritesInFlight--;
                  }
                  if (postWriteRunnable != null) {
                      postWriteRunnable.run();
                  }
              }
          };
  
          final boolean isFromSyncCommit = (postWriteRunnable == null);
  
          // Typical #commit() path with fewer allocations, doing a write on
          // the current thread.
          if (isFromSyncCommit) {
              boolean wasEmpty = false;
              synchronized (XmlStorage.this) {
                  wasEmpty = mDiskWritesInFlight == 1;
              }
              if (wasEmpty) {
                  writeToDiskRunnable.run();
                  return;
              }
          }
  
          QueuedWork.singleThreadExecutor().execute(writeToDiskRunnable);
      }