Move the quic_use_common_stream_check flag count to a location that may be executed in production GFEs instead of a test-only location, and enable the flag in locations that are not reachable in production GFEs. gfe-relnote: n/a (Test and client only change) PiperOrigin-RevId: 285017312 Change-Id: I596f94a6ebb28c90f990f8f8b9ed1aa08afd79ef