Runtime flags for Crosswalk

I'm looking for feedback here. I used the Run As Service, SysApps RawSockets and DeviceCapabilities as an example on how to use the system.

A quick reminder on why we need that :
- Our developers can turn off/on features if they want to by passing it as an argument to the command line
- We can turn off a feature in a given release cycle, beta for example if we feel that the feature won't be ready by the time it will reach stable (this is better than reverting patches).

Future : I plan to add a generic -enable-xwalk-experimental-features which will turn ON all the experimental features (a bit like Chromium) so we can turn that on on our Canary build (just like Chromium so we can get early feedback on some features) but not in beta or stable.

When this feature has landed, I'm going to add more runtime flags for previous work and I plan to make mandatory to add a feature flag for any new feature development (can be JS exposed API or features related to the runtime).

Thoughts?