[omnibox] Accessibility announcements for un/focus tab switch button

We were doing some of the work to generate accessibility
announcements when "focusing" the tab switch button, but not all those
necessary for MacOS. This CL attempts to fill in some of those gaps.

Notably, the tab switch button will have to make its own call to the
accessibility device on focus, and will have to manufacture a
notification when focus returns to the result-view proper.

TBR: [email protected]
Bug: 853929
Change-Id: I8d81a8fa6a6528bb12c5e0ba3faff716610410b6
Reviewed-on: https://chromium-review.googlesource.com/1185300
Commit-Queue: Kevin Bailey <[email protected]>
Reviewed-by: Aaron Leventhal <[email protected]>
Reviewed-by: Justin Donnelly <[email protected]>
Cr-Commit-Position: refs/heads/master@{#589098}
diff --git a/components/omnibox_strings.grdp b/components/omnibox_strings.grdp
index 8a052c8..e6fd35a 100644
--- a/components/omnibox_strings.grdp
+++ b/components/omnibox_strings.grdp
@@ -93,8 +93,15 @@
   <message name="IDS_ACC_AUTOCOMPLETE_N_OF_M" desc="Text for screenreaders describing the current matche's position in the list of suggestions.">
     <ph name="FRIENDLY_MATCH_TEXT">$1<ex>The Chromium Projects http://www.chromium.org bookmark</ex></ph>, <ph name="MATCH_POSITION">$2<ex>2</ex></ph> of <ph name="NUM_MATCHES">$3<ex>3</ex></ph>
   </message>
-  <!-- Accessibility suffix for suggestions with a tab switch match. Comma is important. -->
+  <!-- Accessibility suffix for suggestions with a tab switch match. Commas are important as they add pauses. -->
   <message name="IDS_ACC_TAB_SWITCH_SUFFIX" desc="Suffix for tab switch suggestions to explain keystroke used to switch.">
     <ph name="TAB_SWITCH_SUFFIX">$1, currently open, press tab then enter to switch to the open tab</ph>
   </message>
+  <!-- Accessibility prefix for suggestions where the tab switch button is focused. Commas are important as they add pauses. -->
+  <message name="IDS_ACC_TAB_SWITCH_BUTTON_FOCUSED_PREFIX" desc="Announcement when tab switch button focused.">
+    <ph name="TAB_SWITCH_FOCUSED_FRIENDLY_MATCH_TEXT">Tab switch button, press enter to switch to the open tab, $1<ex>The Chromium Projects http://www.chromium.org bookmark</ex></ph>
+  </message>
+  <message name="IDS_ACC_TAB_SWITCH_BUTTON" desc="Announcement when tab switch button focused.">
+    Tab switch button, press enter to switch to this tab
+  </message>
 </grit-part>