Merge "Document restricted app private file permissions" into mnc-mr-docs

      <li><a href="#bg-opt">Background Optimizations</a></li>

    </ol>

  </li>

  <li><a href="#perm">Permissions Changes</a></li>

  <li><a href="#perm">Permissions Changes</a>

    <ol>

      <li><a href="#permfilesys">File System Permission Changes</a></li>

    </ol>

  </li>

  <li><a href="#accessibility">Accessibility Improvements</a>

    <ol>

      <li><a href="#screen-zoom">Screen Zoom</a></li>

</ul>

<h3 id="permfilesys">File system permission changes</h3>

<p>

  In order to improve the security of private files, the private directory of

  apps targeting Android N or higher has restricted access (0700). This prevents

  leakage of metadata of private files, such as their size or existence. This

  has multiple side effects:

</p>

<ul>

  <li>

    Private files’ file permissions can no longer be relaxed by the owner, and

    an attempt to do so using

    {@link android.content.Context#MODE_WORLD_READABLE} and/or

    {@link android.content.Context#MODE_WORLD_WRITEABLE}, will trigger a

    {@link java.lang.SecurityException}.

  </li>

  <li>

    Passing <code>file://</code> URIs outside the package domain may leave the

    receiver with an unaccessible path. Therefore, attempts to pass a

    <code>file://</code> URI trigger a

    <code>FileUriExposedException</code>. The recommended way to share the

    content of a private file is using the {@link

    android.support.v4.content.FileProvider}.

  </li>

  <li>

    The {@link android.app.DownloadManager} can no longer share privately

    stored files by filename. Legacy applications may end up with an

    unaccessible path when accessing {@link

    android.app.DownloadManager#COLUMN_LOCAL_FILENAME}. Apps targeting

    Android N or higher trigger a {@link java.lang.SecurityException} when

    attempting to access

    {@link android.app.DownloadManager#COLUMN_LOCAL_FILENAME}.

    Legacy applications that set the download location to a public location by

    using

    {@link

    android.app.DownloadManager.Request#setDestinationInExternalFilesDir} or

    {@link

    android.app.DownloadManager.Request#setDestinationInExternalPublicDir}

    can still access the path in

    {@link android.app.DownloadManager#COLUMN_LOCAL_FILENAME}, however, this

    method is strongly discouraged. The preferred way of accessing a file

    exposed by the {@link android.app.DownloadManager} is using

    {@link android.content.ContentResolver#openFileDescriptor}.

  </li>

</ul>

<h2 id="accessibility">Accessibility Improvements</h2>