Bug 1979469 [wpt PR 53987] - [soft navs] Track paints before URL change for PrePaint attribution mode, a=testonly

Automatic update from web-platform-tests
[soft navs] Track paints before URL change for PrePaint attribution mode

Soft Navigation detection currently limits paint tracking to the context
associated with the current URL (not including initial URL), which it
does for efficiency since determining attribution in the advanced (lazy)
attribution mode involves a DOM walk. But this can be inaccurate, and
we'd like to remove this restriction. Since performance is hopefully
fixed by the PrePaint attribution mode (still needs to be proved out
experimentally), and there is relatively little additional overhead in
this mode of tracking pre-URL-change paints, this CL enables that in
this mode.

Most of the heavy lifting was done in crrev.com/c/6779158, and now that
SoftNavigationHeuristics supports computing FCP for all painted contexts
and emitting buffered LCP on entry emission, recording paints before URL
change is just a matter of not limiting
MaybeGetSoftNavigationContextForTiming() to the context for the current
URL.

Bug: 423670827, 434130450
Change-Id: I14656312f5c589163982a0dc68c109362c9aa15e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6778273
Reviewed-by: Michal Mocny <mmocnychromium.org>
Reviewed-by: Philip Rogers <pdrchromium.org>
Reviewed-by: Johannes Henkel <johanneschromium.org>
Commit-Queue: Scott Haseley <shaseleychromium.org>
Cr-Commit-Position: refs/heads/main{#1492331}

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wpt-commits: 84217313d70a298fb95335d6e57bf7d72da70168
wpt-pr: 53987

UltraBlame original commit: fb5f28535a6fe4b7fd1717a3a65477f3e1a076fd

Author: marco-c