Add tooltip to the new context menu button in the touch-select mode.

TEST=manually verified

Bug: 745488
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I1066f0d7b11204db6b18ddaa0e92ec39fa5cd268
Reviewed-on: https://chromium-review.googlesource.com/575806
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Reviewed-by: Naoki Fukino <fukino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488512}

chrome/app/chromeos_strings.grdp

@@ -1181,6 +1181,9 @@ Press any key to continue exploring.
   <message name="IDS_FILE_BROWSER_GEAR_BUTTON_TOOLTIP" desc="Tooltip for the gear button in the Files app.">
     Settings
   </message>
+  <message name="IDS_FILE_BROWSER_SELECTION_MENU_BUTTON_TOOLTIP" desc="Tooltip for the button to open the context menu of currently selected items in the Files app.">
+    More...
+  </message>
 
   <message name="IDS_FILE_BROWSER_TIME_TODAY" desc="File date and time in case the date is today.">
     Today <ph name="TODAY_DAYTIME">$1<ex>6:19 AM</ex></ph>

chrome/browser/chromeos/extensions/file_manager/private_api_strings.cc

@@ -502,6 +502,8 @@ ExtensionFunction::ResponseAction FileManagerPrivateGetStringsFunction::Run() {
   SET_STRING("SHARE_BUTTON_TOOLTIP", IDS_FILE_BROWSER_SHARE_BUTTON_TOOLTIP);
   SET_STRING("SORT_BUTTON_TOOLTIP", IDS_FILE_BROWSER_SORT_BUTTON_TOOLTIP);
   SET_STRING("GEAR_BUTTON_TOOLTIP", IDS_FILE_BROWSER_GEAR_BUTTON_TOOLTIP);
+  SET_STRING("SELECTION_MENU_BUTTON_TOOLTIP",
+             IDS_FILE_BROWSER_SELECTION_MENU_BUTTON_TOOLTIP);
   SET_STRING("GET_INFO_BUTTON_LABEL", IDS_FILE_BROWSER_GET_INFO_BUTTON_LABEL);
   SET_STRING("HOSTED_OFFLINE_MESSAGE", IDS_FILE_BROWSER_HOSTED_OFFLINE_MESSAGE);
   SET_STRING("HOSTED_OFFLINE_MESSAGE_PLURAL",

ui/file_manager/file_manager/main.html

@@ -375,10 +375,11 @@
         <files-toggle-ripple></files-toggle-ripple>
         <div class="icon"></div>
       </button>
-      <!-- TODO(yamaguchi): Set a proper tooltip. -->
       <button id="selection-menu-button" class="icon-button" tabindex="19"
-              menu="#file-context-menu" aria-activedescendant="file-context-menu"
-              hidden>
+              menu="#file-context-menu"
+              i18n-values="aria-label:SELECTION_MENU_BUTTON_TOOLTIP"
+              aria-activedescendant="file-context-menu"
+              has-tooltip hidden>
         <files-toggle-ripple></files-toggle-ripple>
         <div class="icon"></div>
       </button>