[JM] Permit CC PrepareToDraw / DrawLayers lifecycle for TreesInViz feature

Many cc_unittests expect to be able to call PrepareToDraw and DrawLayers
directly. We won't draw layers directly in TreesInViz mode, but we still
need to run much of the Draw lifecycle. Instead of DCHECKing, update these
methods to support TreesInViz mode.

This fixes 324 out of 448 remaining cc_unittest failures.

In a follow up I think it will be good to merge LTHI::UpdateDisplayTree
with the existing Draw lifecycles.

Bug: 383016428
Change-Id: I4ee9d206ab04823f7623218812cb0653a555c114
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6166217
Reviewed-by: Jonathan Ross <jonross@chromium.org>
Commit-Queue: Victor Miura <vmiura@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1404997}