[LargestContentfulPaint] Add attributes and checks

This CL adds checks so that we do not expose rendering timestamp of
images which do not pass the Timing Allow Origin check. It also adds
attributes found in:
https://wicg.github.io/largest-contentful-paint/#sec-performance-largest-contentful-paint-candidate

The ImagePaintTimingDetector did not plumb the ImageResourceContent to
the ImageRecord, so this is fixed to allow LCP Calculator to make use of
it.

Bug: 965505
Change-Id: I019658dc6d130c8cea336f1ca70de6a32beebbb0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674588
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#674085}