
Include Dataspec.httpRequestHeaders in CronetDataSource, and OkHttpDataSource. Updated documentation of HttpDataSource.open() to suggest that it should set request headers (in decreasing priority) from (1) the passed DataSpec, (2) parameters set with setRequestProperty() and (3) default parameters set in the HttpDataSource.Factory. No mechanism has been put in place to enforce this. PiperOrigin-RevId: 266895574