Expose ShouldSwapProcessesForNavigation as API

[zcbenz]

Due to Chromium's issue 126064 http://code.google.com/p/chromium/issues/detail?id=126064, reloading will cause memory leaks on some pages, so users need a way to force restarting the renderer process to avoid memory increasing infinitely.

One way is to overload ContentBrowserClient::ShouldSwapProcessesForNavigation to tell Chromium to start a new renderer process when navigating, but CEF didn't expose it in its API, a corresponding API in CEF would be very helpful.

[magreenblatt]

Sounds reasonable. Please add an issue to the CEF issue tracker.