Clear histogram-span brushedRange on click.
Clear histogram-span brushedRange on click.

Currently, there is no way to clear a brushedRange in histogram-span.
This CL allows users to click in order to clear a brushedRange.

I tried adding a click event handler to ChartBase2D, but it didn't work
because histogram-span sets brushedRange on mousedown and mouseup,
which causes ChartBase2D to draw a rect under the mouse, which causes the mouseup
event to target a different element from the mousedown event, which prevents the
click event from firing.

So this CL adds a bit of hysteresis so that histogram span can say
"On mouseup, if there was one brushed bin before mousedown, and there is only
one new brushed bin, and they are the same bin, then it's probably a click
intended to clear the brushed range."

BUG=catapult:#2846

Review-Url: https://codereview.chromium.org/2492023003

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