Implementations of chrome.system.* for ios (cpu, display, memory, network)

- Add auto tests for chrome.system.cpu plugin
- Initial stub implementation of chrome.system.cpu.getInfo for ios
- Add auto tests for chrome.system.display plugin
- Implementation of chrome.system.display.getInfo for ios
There is no implementation to list the cpu features.  Of course, this is missing on Android as well.  After discussion, we decided that it's acceptable to leave the features un-implemented.  So, I'll mark it as stable on iOS.