Cast: Let the extension control if DSCP is on or off.

Extension now has to call udptransport->setOptions(":DSCP") to get dscp set.

This framework should also let us experiment with different wifi settings in windows and different pacing settings.

Review URL: https://codereview.chromium.org/551883004

Cr-Commit-Position: refs/heads/master@{#294211}

• chrome/browser/media/cast_transport_host_filter.cc[diff]
• chrome/browser/media/cast_transport_host_filter.h[diff]
• chrome/browser/media/cast_transport_host_filter_unittest.cc[diff]
• chrome/common/cast_messages.h[diff]
• chrome/common/extensions/api/cast_streaming_udp_transport.idl[diff]
• chrome/renderer/extensions/cast_streaming_native_handler.cc[diff]
• chrome/renderer/extensions/cast_streaming_native_handler.h[diff]
• chrome/renderer/media/cast_session.cc[diff]
• chrome/renderer/media/cast_session.h[diff]
• chrome/renderer/media/cast_session_delegate.cc[diff]
• chrome/renderer/media/cast_session_delegate.h[diff]
• chrome/renderer/media/cast_transport_sender_ipc.cc[diff]
• chrome/renderer/media/cast_transport_sender_ipc.h[diff]
• chrome/renderer/media/cast_udp_transport.cc[diff]
• chrome/renderer/media/cast_udp_transport.h[diff]
• media/cast/net/cast_transport_sender.h[diff]
• media/cast/net/cast_transport_sender_impl.cc[diff]
• media/cast/net/cast_transport_sender_impl.h[diff]
• media/cast/net/cast_transport_sender_impl_unittest.cc[diff]
• media/cast/sender/audio_sender_unittest.cc[diff]
• media/cast/sender/video_sender_unittest.cc[diff]
• media/cast/test/cast_benchmarks.cc[diff]
• media/cast/test/end2end_unittest.cc[diff]
• media/cast/test/sender.cc[diff]
• media/cast/test/simulator.cc[diff]