[quickview] date-time-format-changed should not redraw metadata box

The 'date-time-format-changed' event fires when the user's system date
and time preferences change.

This event causes the metadata box to do a complete draw cycle: clear,
metadata fetch, and draw. However, the only thing that needs to change
visually is the format of the modificationTime. Do just that only, and
this to avoid re-draw flash.

Change-Id: I6392fef41912e78c57805a6dc018a55f89fe7b69
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1682963
Commit-Queue: Noel Gordon <noel@chromium.org>
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673657}