A WebChannelTransport instance represents a shared context of logical
connectivity between a browser client and a remote origin.
Over a single WebChannelTransport instance, multiple WebChannels may be
created against different URLs, which may all share the same
underlying connectivity (i.e. TCP connection) whenever possible.
When multi-domains are supported, such as CORS, multiple origins may be
supported over a single WebChannelTransport instance at the same time.
Sharing between different window contexts such as tabs is not addressed
by WebChannelTransport. Applications may choose HTML5 shared workers
or other techniques to access the same transport instance
across different window contexts.