Chrome Version       : 51.0.2704.84
OS Version: OS X 10.11.4
ChromeVox Version    : 50.0.2661.83
URLs (if applicable) : https://github.com/blog/122-embedded-gists
Other browsers tested: N/A (ChromeVox issue)

What steps will reproduce the problem?
1. Enable ChromeVox
2. Navigate to the URL above
3. Within the page, set focus to the paragraph above the embedded gist/iframe. Sighted users can click the paragraph to move focus
4. From the paragraph above the iframe use *ChromeVox + Left Arrow* key shortcut to navigate to the iframe

What is the expected result?

ChromeVox should read the first thing (based on specificity settings) within the iframe's document.

What happens instead of that?

ChromeVox reads the element's inner html (from source) which is used to provide alternative content for browsers which do not support iframes. In this case, the content is "Your browser does not support IFrames" (see below HTML source). When navigating with *ChromeVox + Up Arrow* and *ChromeVox + Down Arrow* the user is correctly navigated into the iframe document.

Please provide any additional information below. Attach a screenshot if
possible.

Applicable HTML source:

  <iframe src="https://gist.github.com/defunkt/2059.pibb?scroll=true" style="height: 214px">Your browser does not support IFrames</iframe>

UserAgentString: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.84 Safari/537.36