A Unity editor script to get all filenames (and file sizes) in the project and save them in a .txt file as a list.

DldUtil_DumpFilenames.cs

using UnityEngine;
using UnityEditor;
using System.Collections;
using System.IO;

namespace DldUtil
{

public class DumpFilenames
{

#if UNITY_EDITOR
	[MenuItem("Window/Dump filenames of assets")]
	public static void Dump()
	{
		string dumpFilename = EditorUtility.SaveFilePanel(
				"Save dump to",
				"",
				"FileDump", "txt");

		string folder = Application.dataPath;

		Debug.Log("Dumping from: " + folder);

		bool canceled = false;


		System.IO.Directory.CreateDirectory(System.IO.Path.GetDirectoryName(dumpFilename));
		System.IO.StreamWriter write = System.IO.File.CreateText(dumpFilename);


		foreach (string file in TraverseDirectory.Do(folder))
		{
			canceled = EditorUtility.DisplayCancelableProgressBar("Dumping from " + folder, file, 0.5f);
			if (canceled)
			{
				write.Write("\tCanceled by user\n");
				Debug.Log("Dumping canceled by user");
				break;
			}

			string fileRelativePath = file.Replace(folder, "");
			long sizeInBytes = GetFileSizeInBytes(file);
			write.Write(fileRelativePath + "\t" + sizeInBytes + "\n");
		}

		Debug.Log("Dumping complete");
		write.Close();

		EditorUtility.ClearProgressBar();
	}
#endif

	static long GetFileSizeInBytes(string filename)
	{
		FileInfo fi = new FileInfo(filename);
		return fi.Length;
	}
}

} // namespace DldUtil