Cef 2171 - Upgrade to Chromium 39

PR based around merging `cef/2171` branch into `master`, when it's time to upgrade to `Chromium 39`.

Feel free to discuss any changes/improvements you'd like to see.

Currently this branch is **experimental** and should only be used by advanced `CefSharp`.

Laundry list of outstanding changes

- Cleanup `OSR` Rendering code and refactor into pluggable implementation
- Cleanup `SchemaHandler`, fixing #680 
- Upgrade to latest `Cef` version
- Continued code cleanups