cc: edchin. It would be great if you have time to take a look at this (until sczs is back).

I have a fix for this and was waiting on Louis to come back and take a look 
https://codereview.chromium.org/2605023002/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c0d82cf0179b873629fb2cbf2c253e9edc591920

commit c0d82cf0179b873629fb2cbf2c253e9edc591920
Author: sczs <sczs@google.com>
Date: Thu Jan 05 16:38:26 2017

Prevents history navigation items from being voice-over selectable while not visible.

Removing accessibility traits for these navigation items or disabling them, didn't
prevent them from being voice-over selectable while not visible due to the search bar
being presented on top.

Setting the view's accessibilityViewIsModal to YES fixed the problem but prevented
the history results from being voice-over selectable.

For these reasons the current approach was used.

BUG= 674891 

Review-Url: https://codereview.chromium.org/2605023002
Cr-Commit-Position: refs/heads/master@{#441672}

[modify] https://crrev.com/c0d82cf0179b873629fb2cbf2c253e9edc591920/ios/chrome/browser/ui/history/history_panel_view_controller.mm

CL Link: https://codereview.chromium.org/2605023002/

[Auto-generated comment by a script] We noticed that this issue is targeted for M-56; it appears the fix may have landed after branch point, meaning a merge might be required. Please confirm if a merge is required here - if so add Merge-Request-56 label, otherwise remove Merge-TBD label. Thanks.

This bug requires manual review: Less than 2 weeks to go before AppStore submit on M56
Please contact the milestone owner if you have questions.
Owners: amineer@(clank), cmasso@(bling), gkihumba@(cros), bustamante@(desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

 pmadalla@ please verify this issue is fixed in the latest canary.

Verified in 57.0.2974.0 canary, iPad Air iOS 9.3.5

This issue has been approved for a merge. Please merge the fix to any appropriate branches as soon as possible!

If all merges have been completed, please remove any remaining Merge-Approved labels from this issue.

Thanks for your time! To disable nags, add the Disable-Nags label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/chrome/ios_internal.git/+/b25c5f74590d53a95eac0908d5d84b359ce86111

commit b25c5f74590d53a95eac0908d5d84b359ce86111
Author: sczs <sczs@google.com>
Date: Wed Jan 11 11:54:00 2017

Verified on latest chrome beta version 56.0.2924.66 on iPhone 6s with iOS 10.2 and iPad Air with iOS 10.1.1, following the steps mentioned in comment #0.  Backgrounded text is not read with voice over : on.  Looks good.