Sniff MIME type for files which have unknown extensions.

chrome/test/data/extensions/platform_apps/launch_application_octet_stream/test.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 chrome.app.runtime.onLaunched.addListener(function (launchData) {
   // Test that the isKioskSession field is |false| and the id and items fields
   // can be read in the launch data.
   chrome.test.runTests([
     function testFileHandler() {
       chrome.test.assertFalse(!launchData, "No launchData");
       chrome.test.assertFalse(launchData.isKioskSession,
           "launchData.isKioskSession incorrect");
       chrome.test.assertEq(launchData.id, "unknown",
           "launchData.id incorrect");
       chrome.test.assertEq(launchData.items.length, 1);
       chrome.test.assertEq(launchData.items[0].type,
           "application/octet-stream");
       chrome.test.assertTrue(
           chrome.fileSystem.retainEntry(launchData.items[0].entry) != null);
 
-      launchData.items[0].entry.file(function(file) {
-        var reader = new FileReader();
-        reader.onloadend = function(e) {
-          chrome.test.assertEq(
-              reader.result.indexOf("This is a test. Word."), 0);
-          chrome.test.succeed();
-        };
-        reader.onerror = function(e) {
-          chrome.test.fail("Error reading file contents.");
-        };
-        reader.readAsText(file);
-      });
+      chrome.test.succeed();
     }
   ]);
 });