Closure Performance Tests - goog.pubsub.PubSub

# goog.pubsub.PubSub Performance Tests

User-agent:

Compares the performance of the event system (`goog.events.*`) with the `goog.pubsub.PubSub` class.

The baseline test creates 1000 event targets and 1000 objects that handle events dispatched by the event targets, and has each event target dispatch 2 events 5 times each.

The single-`PubSub` test creates 1000 publishers, 1000 subscribers, and a single pubsub channel. Each subscriber subscribes to topics on the same pubsub channel. Each publisher publishes 5 messages to 2 topics each via the pubsub channel.

The multi-`PubSub` test creates 1000 publishers that are subclasses of `goog.pubsub.PubSub` and 1000 subscribers. Each subscriber subscribes to its own publisher. Each publisher publishes 5 messages to 2 topics each via its own pubsub channel.