We can easily announce that new tab was selected, but if we give focus to the toolbar (which is the top view) Talk Back will announce different things depending on which view is being shown. For Downloads, it will announce "Dropdown list downloads. Double tap to change." since downloads has a spinner as it's first element. For bookmarks, it will announce the title of the current folder since that's what's shown in the toolbar. For history, it will announce "History".

I propose that we announce which tab was selected without trying to give focus to the toolbar.

Yes, I'm fine with that solution. It's what Google Photos does. Feel free to disagree Laura.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/44dd1fe909c433cf0b8297be8825e372fc2d57a8

commit 44dd1fe909c433cf0b8297be8825e372fc2d57a8
Author: twellington <twellington@chromium.org>
Date: Tue May 23 18:36:17 2017

[Home] Add some accessibility support

 * Announce when the panel is opened and closed.
 * Prevent focus from going to the tab content when the bottom
   sheet is open.
 * Change the in-product help bubble when the expand button is
   enabled and use different strings for non-accessibility mode
   and accessibility mode.
 * Announce when a different bottom sheet tab is selected.
 * When the expand button isn't visible, make the entire toolbar
   focusable for accessibility and add a content description.

BUG= 724694 , 724696 , 724693 , 724695 

Review-Url: https://codereview.chromium.org/2895223003
Cr-Commit-Position: refs/heads/master@{#473995}

[modify] https://crrev.com/44dd1fe909c433cf0b8297be8825e372fc2d57a8/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
[modify] https://crrev.com/44dd1fe909c433cf0b8297be8825e372fc2d57a8/chrome/android/java/src/org/chromium/chrome/browser/toolbar/BottomToolbarPhone.java
[modify] https://crrev.com/44dd1fe909c433cf0b8297be8825e372fc2d57a8/chrome/android/java/src/org/chromium/chrome/browser/widget/bottomsheet/BottomSheet.java
[modify] https://crrev.com/44dd1fe909c433cf0b8297be8825e372fc2d57a8/chrome/android/java/src/org/chromium/chrome/browser/widget/bottomsheet/BottomSheetContentController.java
[modify] https://crrev.com/44dd1fe909c433cf0b8297be8825e372fc2d57a8/chrome/android/java/strings/android_chrome_strings.grd

Verified on M60-60.0.3112.0 build

I'm going to re-open to track an add on piece for accessibility. We should change the toolbar content description to "pull down to close navigation panel" or something like that when the sheet is opened.

This was the wrong bug to re-open.  Issue 724695  is about telling users the toolbar is swipeable.