[Streams] Prototype a Streams API compatible PresentationConnection

[markafoltz]

In Issue #163 @domenic and I discussed the possibility for adding Streams-compatible APIs for messaging to the PresentationConnection. While it looks like timelines don't line up to add this work directly to the spec, we should experiment with polyfills for this behavior so that when Streams is ready for implementation we already have an idea of what APIs would work well.

Benefits of Streams:

• Type-agnostic messaging
• Congestion control and backpressure
• Push/pull compatible
• Transform APIs
• etc.

[markafoltz]

@domenic There may also be a possibility for a Stream (or MediaStream) to be piped from the controller to the presentation, or vice versa. For example a Stream or MediaStream generating API like getUserMedia, PeerConnection, or Sensors could be used for remote control or media rendering.

Stream passing between contexts would allow the user agent to route events more efficiently than having the page install an event handler in script and serializing the events as string or binary messages.