Now that double-tap reflow-on-zoom has landed, we need to be a bit more careful about how the position maintenance code for reflow-on-zoom happens and which events trigger it. This patch removes the code that previously did position maintenence for reflow-on-zoom during a pinch-zoom event, but adds back the onPinchFinish() handler so that when pinch-zooming out, we can reset the max line box width if it changed due to a double-tap zoom event previously encountered.
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