Expose Request Contexts and Chromium Preferences (lots of new settings that can be set during runtime)

[cztomczak]

Lots of new settings can be set using CefRequestContext.SetPreference. Full list of preference names can be found in upstream Chromium pref_names.cc files:

• Common: https://cs.chromium.org/chromium/src/chrome/common/pref_names.cc
• More pref_names.cc files spread across Chromium sources: https://cs.chromium.org/search/?q=pref_names.cc+package:%5Echromium$&type=cs

Upstream issue that added the Preferences feature:
https://bitbucket.org/chromiumembedded/cef/issues/1709/allow-configuration-of-preferences-during

CefRequestContext related methods:

• GetAllPreferences - all preferences for browser's request context
• SetPreference
• many more methods has/get/canset...

Other context settings via _cef_request_context_settings_t:

• cache_path
• persist_session_cookies
• persist_user_preferences
• ignore_certificate_errors

Provide common preferences examples in API docs.

Example preferences:

• "proxy" => {"mode": "fixed_servers", "server": "127.0.0.1:8888"} # or "scheme://host:port"
• "webkit.webprefs.plugins_enabled" => True

Maybe expose useful/common preferences via ApplicationSettings / BrowserSettings? See example preferences:

• CEF4Delphi project: https://github.com/salvadordf/CEF4Delphi/blob/381f43394b1b52fb2384803562bb7d2aae800d1e/source/uFMXChromium.pas#L1890 (also check latest from master)
• CefSharp project: ...

All CEF preferences can be seen by running http://tests/preferences.html url in cefclient sample application as seen in the screenshot below. To get a list of all preferences programmatically call CefRequestContext.GetAllPreferences method.