Gets the local description for this connection, waiting until gathering is complete to provide a full result. Because this waits for gathering, it will not resolve if no DataChannel, other tracks or remote description have been provided beforehand.
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An RTC connection is a single connection. This base class defines the raw connection management and tracking logic for a generic connection. The MockRTCConnection subclass extends this and adds logic to support control channels, proxying and other MockRTC-specific additions.