webrtc-51c367e

libwebrtc build from webrtc-sdk/webrtc@51c367e (m150_release).

Ships the external_audio_source.patch fix from #1491 by @richard134. After an unpublish and renegotiation, a NativeAudioSource send stream could be registered with AudioState and never removed, so the capture thread called into a freed stream once the PeerConnection closed. This is the crash reported in #1490.

Also picks up the webrtc-sdk/webrtc commits on m150_release since 89d790b404 (the webrtc-89d790b build):

• webrtc-sdk/webrtc#284 Guard simulcast-factory AV1 advertisement, fail fast on nil ObjC encoder/decoder
• webrtc-sdk/webrtc#285 Ship missing ObjC headers in the mac framework
• webrtc-sdk/webrtc#286 Do not instantiate AVAudioEngine.inputNode on playout-only engine teardown
• webrtc-sdk/webrtc#283 Expose enableSctpSnap on RTCConfiguration (ObjC and Android) for WARP
• webrtc-sdk/webrtc#290 Update README with upstream and release info
• webrtc-sdk/webrtc#288 android: do not assert when prewarmRecording runs after a failed recorder init
• webrtc-sdk/webrtc#295 Query VideoToolbox H.264 profile levels lazily instead of in a static initializer
• webrtc-sdk/webrtc#301 Fail AddTransceiver with INVALID_STATE on a closed PeerConnection
• webrtc-sdk/webrtc#297 Verify server-injected frame payloads before skipping decryption
• webrtc-sdk/webrtc#311 Prevent raw_key/derived_key from leaking via LS_INFO

Build script changes since webrtc-89d790b: #1456 (Android jar class version) and #1494 (fail the build when a patch does not apply).