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- Remove 2 member variables and 2 methods from AXObject, which were used
so that AXObject could calculate whether ignored changed.
- Remove repetitive code from AXObjectCacheImpl, whenever an
AXObject is created.

Bug: None
Change-Id: Iad38383819dd1d165169fd302a717f3e2bacb2b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2383813
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803250}