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While deserializing, make a note of all changed nodes via id before performing any tree changes/removals.

While removing (non-atomically), reference the changed list to ensure we notify delegates of nodes that will actually be deleted and not just deleted then re-created as part of bookkeeping to enforce the "non-reparenting" invariant inside of AXTree::CreateChildVector.

BUG=642799
TEST=for each of the reproductions in the bug, ensure the automation api (as a client) does not destroy then re-create js objects; rather, ensure it re-uses them for reparented trees.

Review-Url: https://codereview.chromium.org/2080573003
Cr-Commit-Position: refs/heads/master@{#417207}