My first thought is to check here:

ui/views/accessibility/ax_view_obj_wrapper.cc

In AXViewObjWrapper::Serialize:

Instead of view_->IsFocusable(), try view_->IsAccessibilityFocusable(), that should return true more often

Then instead of (!view_->visible()), try (!view_->IsDrawn()), that should also handle the cases where the view's parent or another ancestor isn't visible

See how many that fixes. Whatever's left, let's fix the specific buttons.

Changing to view_.IsAccessibilityFocusable() fixes everything except individual tabs, so accounting for that separately.

!view_->IsDrawn() didn't seem to fix anything, and appeared to act less consistently than visible(), so leaving as !view_->visible().

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/db7f879ab02ada7f66b0aa955d1658482cc3af2c

commit db7f879ab02ada7f66b0aa955d1658482cc3af2c
Author: elichtenberg <elichtenberg@google.com>
Date: Wed Apr 12 22:48:52 2017

Improved isInteresting heuristic, made more AutomationNodes focusable

BUG=593885, 710559 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2818503002
Cr-Commit-Position: refs/heads/master@{#464184}

[modify] https://crrev.com/db7f879ab02ada7f66b0aa955d1658482cc3af2c/chrome/browser/resources/chromeos/switch_access/switch_access.js
[modify] https://crrev.com/db7f879ab02ada7f66b0aa955d1658482cc3af2c/chrome/browser/resources/chromeos/switch_access/tree_walker.js
[modify] https://crrev.com/db7f879ab02ada7f66b0aa955d1658482cc3af2c/chrome/browser/resources/chromeos/switch_access/tree_walker_unittest.gtestjs
[modify] https://crrev.com/db7f879ab02ada7f66b0aa955d1658482cc3af2c/ui/views/accessibility/ax_view_obj_wrapper.cc

All of the actions listed in the initial bug are not actionable with Switch Access.

* now actionable with Switch Access