All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=817133

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=fa288b979aa77a3e4f8279d846e327acb61f4bafb10a789a1a78ce56df8d043a


Bot(s) for this bug's original alert(s):

chromium-rel-win7-x64-dual

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/14936b24440000

The two spikes in perf match perfectly with this change:

Add hooks for AXTreeDelegate when a relation target changes

Originally landed as r534885
https://chromium-review.googlesource.com/c/chromium/src/+/899862
Then relanded as r537636
https://chromium-review.googlesource.com/c/chromium/src/+/924769

The first change was reverted because we caught the performance issues. I think we solved the issue for the reland by excluding firing events for nodes created, but there might be another issue not caught by the perf tests. 

Perhaps we need to introduce a boolean accessibility attribute in the browser tree, HasRelationsToOtherNodes. Now we go through all the int and int-list attributes and check if one if its one of the attributes used for relations or not, and we do this for every update or deletion.

Fix here:

https://chromium-review.googlesource.com/c/chromium/src/+/940815

📍 Found significant differences after each of 3 commits.
https://pinpoint-dot-chromeperf.appspot.com/job/14936b24440000

[Dice] Display accounts submenu in bookmarks bubble by tangltom@chromium.org
https://chromium.googlesource.com/chromium/src/+/676bd99ceb23a17c820a3661a0c07572e6aa5280

Add uma metric for bookmarks JSON file size and time to write by mamir@chromium.org
https://chromium.googlesource.com/chromium/src/+/3df2894f790e335c4947e47f19dc1526f34b96a4

Reland: Fire events on relation sources by dtseng@chromium.org
https://chromium.googlesource.com/chromium/src/+/ef6b480df5da00a479da222bb801596168a9c510

Understanding performance regressions:
  http://g.co/ChromePerformanceRegressions

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cb4c290c4d9c11429d92403e239caebfff09cbc2

commit cb4c290c4d9c11429d92403e239caebfff09cbc2
Author: Dominic Mazzoni <dmazzoni@chromium.org>
Date: Wed Feb 28 08:18:38 2018

Fix performance regression in AXEventGenerator

The reverse relation maps are maps from each attribute, to
a map from destination id to a set of source ids, like this:

  map<attr, map<int, set<int>>>

AXEventGenerator::FireRelationSourceEvents used const auto
in two places where it should have used const auto&, resulting
in making two temporary copies of every entry in the map for
each node in the tree.

Tested manually using chrome://tracing. Without
FireRelationSourceEvents at all, loading one Wikipedia page
took ~100 ms. With FireRelationSourceEvents, it took 28,000 ms.
With this fix it took ~115 ms, so FireRelationSourceEvents is
now adding just a small, acceptable amount of overhead. We could
optimize it further if needed.

Bug:  817133 
Change-Id: Ib02968593ed5c9533fb72adae4eba32faea3e61f
Reviewed-on: https://chromium-review.googlesource.com/940815
Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539757}
[modify] https://crrev.com/cb4c290c4d9c11429d92403e239caebfff09cbc2/ui/accessibility/ax_event_generator.cc

 Issue 813990  has been merged into this issue.

 Issue 814246  has been merged into this issue.

Issue 814750 has been merged into this issue.