[StartSurface] Add accessibility message for incognito toggle

Bug: 1015976
Change-Id: Iffe5eb9fbde4c2abb666f174700699d0025b3c6c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1869711
Auto-Submit: Ganggui Tang <gogerald@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707571}

chrome/android/java/src/org/chromium/chrome/browser/toolbar/top/IncognitoSwitchViewBinder.java

@@ -37,6 +37,11 @@ class IncognitoSwitchViewBinder {
                     : R.string.accessibility_tab_switcher_standard_stack_selected;
             incognitoSwitch.announceForAccessibility(
                     incognitoSwitch.getResources().getString(stackAnnouncementId));
+            final int descriptionResId = isIncognito
+                    ? R.string.accessibility_tabstrip_btn_incognito_toggle_incognito
+                    : R.string.accessibility_tabstrip_btn_incognito_toggle_standard;
+            incognitoSwitch.setContentDescription(
+                    incognitoSwitch.getResources().getString(descriptionResId));
         } else if (IS_VISIBLE == propertyKey) {
             incognitoSwitch.setVisibility(model.get(IS_VISIBLE) ? View.VISIBLE : View.GONE);
         }