On Chrome OS, you can enable spoken feedback (ChromeVox) by pressing Ctrl+Alt+Z.
You can install ChromeVox from the web store, but it may not be the latest version checked into trunk and it won't have the same permissions.
To test the version of ChromeVox that runs on Chrome OS while running a desktop Linux build of Chrome with the chromeos=1 GYP flag, you can just install ChromeVox in /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
Note: ChromeVox requires a NaCl-enabled build!