Update to Chromium revision 248478.
- Add new CefSettings.windowless_rendering_enabled value that must be enabled when using windowless (off-screen) rendering.
- Improve naming and documentation for CefWindowInfo members.
- CefBeginTracing now completes asynchronously.
- Rename CefEndTracingAsync to CefEndTracing.
- Rename CefCompletionHandler to CefCompletionCallback.

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk@1592 5089003a-bbd8-11dd-ad1f-f1f9622dbc98