title: Chrome extension manifest 2 and 1, compatibility
body: <p>I have an extension that I recently upgraded to manifest version 2. To do this I removed the <code>background_page</code> property in the manifest file and replaced it with <code>background: {page: "background.html"}</code>. This works and everything is fine. Turns out, however, that there are browsers and people out there with old versions of Chrome, or versions of Rockmelt and other Chromium-based browsers that don't support the <code>background</code>-property, or the <code>manifest_version: 2</code> yet.</p>
  
  <p>A simple solution would be to just add the <code>background_page: "background.html"</code>-property to the manifest file, in addition to the <code>background</code>-property. This gives the warning in <code>chrome://extension</code> developer mode:</p>
  
  <pre><code>There were warnings when trying to install this extension:
       'background_page' requires manifest version of 1 or lower.
  </code></pre>
  
  <p>My question is: can having both have any negative impact? For example, what will happen when <code>background_page</code> is deprecated? Will my users see any warnings? Any ideas?</p>