Starting a brush may emit a brush event.

[mbostock]

Currently we call emit.start at the start of a brush gesture:

d3-brush/src/brush.js

Line 357 in 8aed2b3

emit.start();

If the brush is already started, then this does not emit a start event. However, it should emit a brush event, because the brush region may have changed.

[mbostock]

Instead of this:

start: function() {
  if (this.starting) this.starting = false, this.emit("start");
  return this;
}

I think we want this:

start: function() {
  if (this.starting) this.starting = false, this.emit("start");
  else this.emit("brush");
  return this;
}