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This adds opaque ToNodeBase functionality to public node types allowing
the NodeAttachedData implementation to avoid specialization for each
known public node type.

BUG=958115

Change-Id: Ib19c07319d43205560fd4086a919abee30cab5d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1597694
Commit-Queue: Chris Hamilton <chrisha@chromium.org>
Reviewed-by: Sigurður Ásgeirsson <siggi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657740}