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When a node is updated, on the browser side we need to
go through a three-phase process to update the hypertext
and other computed Windows attributes.

In some cases we also need to update the parent node's
attributes too - specifically when the original node is
text that contributes to its parent's hypertext, or
in an editable text region where things like spelling
markers need to propagate.

The previous algorithm was essentially that while updating
a node, it'd force its parent to update too. This led to
an inefficiency if you have a very flat document with
thousands of nodes that are all children of a single
parent. Every node that's updated triggers updating its
parent, causing the parent to be updated thousands of
times redundantly.

The fix is to first precompute a set of all nodes that need
to be updated, including following parents, and then
update them all with no more recursion.

This dramatically improves the load time of documents with
thousands of lines of just flat text and line breaks.

Bug: 921789

Change-Id: I5246ea321fda8a6ddce45221377010a4b5543801
Reviewed-on: https://chromium-review.googlesource.com/c/1455858
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629898}