Settings: show placeholder text in search field for the add language dialog

Bug: 705359
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I267391af9bc7bab6fa3c9e5e86f326534ac6ae93
Reviewed-on: https://chromium-review.googlesource.com/1022371Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552465}

chrome/app/settings_strings.grdp

@@ -2161,6 +2161,9 @@
   <message name="IDS_SETTINGS_LANGUAGES_LANGUAGES_LIST_TITLE" desc="Title for the currently used language in the header for the collapsible list of languages.">
     Language
   </message>
+  <message name="IDS_SETTINGS_LANGUAGE_SEARCH" desc="Placeholder/label for the text input field that allows a user to filter languages.">
+    Search languages
+  </message>
   <message name="IDS_SETTINGS_LANGUAGES_EXPAND_ACCESSIBILITY_LABEL" desc="Label for the button that toggles showing the language options. Only visible by screen reader software.">
     Show language options
   </message>

chrome/browser/resources/settings/languages_page/add_languages_dialog.html

@@ -42,7 +42,7 @@
     <cr-dialog id="dialog" close-text="$i18n{close}">
       <div slot="title">$i18n{addLanguagesDialogTitle}</div>
       <div slot="body" scrollable>
-        <settings-subpage-search label="[[searchLabel]]"
+        <settings-subpage-search label="$i18n{searchLanguages}"
             on-search-changed="onSearchChanged_" autofocus>
         </settings-subpage-search>
         <iron-list class="ripple-padding" scroll-target="[[$$('[slot=body]')]]"

chrome/browser/ui/webui/settings/md_settings_localized_strings_provider.cc

@@ -1220,6 +1220,7 @@ void AddLanguagesStrings(content::WebUIDataSource* html_source) {
   LocalizedString localized_strings[] = {
     {"languagesPageTitle", IDS_SETTINGS_LANGUAGES_PAGE_TITLE},
     {"languagesListTitle", IDS_SETTINGS_LANGUAGES_LANGUAGES_LIST_TITLE},
+    {"searchLanguages", IDS_SETTINGS_LANGUAGE_SEARCH},
     {"languagesExpandA11yLabel",
      IDS_SETTINGS_LANGUAGES_EXPAND_ACCESSIBILITY_LABEL},
     {"orderLanguagesInstructions",