[FCP++] TextPaint: report size to Page Load Metrics

Currently we are only reporting time of Largest/Last Text Paint to the Page
Load Metrics. We need to report size as well. This is mainly because of Largest
Content Paint. LCP requires size to decide the largest content, before
reporting the paint time of the largest content. As well, the size info
will make it possible to merge FCP++ based on the size of contents from
iframes.

This CL plumbs the size from TextPaintTimingDetector to PageLoadMetrics.

The change for the image part lives in here:
https://chromium-review.googlesource.com/c/chromium/src/+/1380193

Bug: 915700
Change-Id: I377326c67f909176bca3c2db6881eabf4f614412
Reviewed-on: https://chromium-review.googlesource.com/c/1396597
Commit-Queue: Liquan (Max) Gu <maxlg@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620496}
8 files changed