Browser backends in Telemetry gather command line args for chrome from various sources and then blindly stash them all into a single list.

This causes problems when flags from different sources may conflict with each other (e.g. --disable-features in  issue 799125 ).

For this we propose implementing a smarter "ChromeArgsBuilder" which can validate flags as they are added, group them together if needed and complain if conflicting values are set (e.g. both enabling and disabling the same feature) at the time when the conflicting flag is added.