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Paint invalidation tracking was a good feature. It shows paint
invalidation events in timeline and indicates the reasons (not generic
reasons like "style", "layout", but specific reasons that can link to
the javascript code etc.) However it has a problem that we often fail
to match paint invalidation events to other invalidation events by
node ids to find the reasons, and discard these events. This is
because the paint invalidation caused by style or layout change on
one node may not happen on that node, but on other nodes. This problem
makes the feature incorrect in many cases, and it's hard to fix.
We could show paint invalidation events without specific reasons,
but I doubt how much value that would provide to web developers.

So I'm removing the feature to avoid the maintenance burden.

Change-Id: I2de2135dbb69041683bac49242b5e9bb6484ee02
Bug: 410701
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1661690Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670239}