This time I am committing the protocol changes first and saving the
Observatory changes for a second cl.
------
We currently support 5 streams: Isolate, Debug, GC, _Echo, and _Graph.
Only generate events when at least one client is listening to the
corresponding event stream.
Only send events to the clients that actually request them.
BUG=
R=johnmccutchan@google.com
Review URL: https://codereview.chromium.org//1166433008
Todd Turnidge
996f012707