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This makes pre-CompositeAfterPaint work like CompositeAfterPaint:
only convert DisplayItemList if needed.

This fixes a perforance regression caused by crrev.com/c/2437735
which moved DisplayItemList conversion into Paint document lifecycle
for ease of benchmarking and consistency with CompositeAfterPaint.

Compared to before crrev.com/c/2437735, this CL can also avoid
conversion when cc side needs update but blink side does not (so
the change in recording_source.cc).

Bug: 1134633
Change-Id: I27a899f787c91a809fef5ce8edd663ac2720e0ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2451271
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814949}