Horizontal tab switcher toggle announce for accessibility

Announce for accessibility when the normal or incognito tab stack
is selected.

Bug: 892638
Change-Id: I8ca8e37d8374e5f57e8b4ef5181c05d00322158e
Reviewed-on: https://chromium-review.googlesource.com/c/1265031Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Pedro Amaral <amaralp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597348}

chrome/android/java/src/org/chromium/chrome/browser/toolbar/IncognitoToggleTabLayout.java

@@ -137,5 +137,12 @@ public class IncognitoToggleTabLayout extends TabLayout {
 
         mTabModelSelector.commitAllTabClosures();
         mTabModelSelector.selectModel(incognitoSelected);
+
+        final int stackAnnouncementId = incognitoSelected
+                ? (ChromeFeatureList.isEnabled(ChromeFeatureList.INCOGNITO_STRINGS)
+                                  ? R.string.accessibility_tab_switcher_private_stack_selected
+                                  : R.string.accessibility_tab_switcher_incognito_stack_selected)
+                : R.string.accessibility_tab_switcher_standard_stack_selected;
+        announceForAccessibility(getResources().getString(stackAnnouncementId));
     }
 }