On Chrome OS, you can enable spoken feedback (ChromeVox) by pressing Ctrl+Alt+Z.
To test the version of ChromeVox that runs on Chrome OS while running a desktop Linux, you can build the Chrome OS version of Chrome.
First add chromeos=1 to your GYP_DEFINES. (More info on GYP_DEFINES here)
Now build Chrome as usual, e.g.:
ninja -C out/Release chrome
If you want speech, you just need to copy the speech synthesis data files to /usr/share like it would be on a Chrome OS device:
git clone https://chromium.googlesource.com/chromiumos/platform/assets
sudo mv assets /usr/share/chromeos-assets
for f in *.zip; do sudo unzip $f && rm $f; done
After you do that, just run "chrome" (e.g. out/Release/chrome) and press Ctrl+Alt+Z, and you should hear it speak! If not, check the logs.
To test ChromeVox Next, add #chromevox_next_test to the end of any url
...for example: http://google.com#chromevox_next_test