Support uploading traces created by other platforms into DevTools #2222

Low priority as users can view these traces with other trace viewers. It could be nice to have so that users debugging pproblems reported by users who may not have used chrome devtools can still use the platform they are familiar with.

@kenzieschmoll suggests that if we look for a top level field "traceEvents" we should be able to assume that a v8 format timeline race is a timeline import.