[WebUI] Add PluralStringHandler and PluralStringProxy

This change registers the PluralStringHandler as a MessageHandler for
the SettingsUI and adds PluralStringProxy as a thin JavaScript wrapper
around it.

Bug: 1047726
Change-Id: I4c53eed726711635adb29e63435dd9da697d0635
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2090425Reviewed-by: Esmael Elmoslimany <aee@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747854}

chrome/browser/resources/settings/BUILD.gn

@@ -137,6 +137,7 @@ js_type_check("settings_resources") {
     ":metrics_browser_proxy",
     ":open_window_proxy",
     ":page_visibility",
+    ":plural_string_proxy",
     ":route",
     ":router",
     ":search_settings",
@@ -173,6 +174,10 @@ js_library("open_window_proxy") {
   deps = [ "//ui/webui/resources/js:cr" ]
 }
 
+js_library("plural_string_proxy") {
+  deps = [ "//ui/webui/resources/js:cr" ]
+}
+
 js_library("route") {
   deps = [
     ":page_visibility",
@@ -474,6 +479,7 @@ js_modulizer("modulize") {
     "lifetime_browser_proxy.js",
     "metrics_browser_proxy.js",
     "open_window_proxy.js",
+    "plural_string_proxy.js",
     "page_visibility.js",
     "route.js",
     "router.js",

chrome/browser/resources/settings/plural_string_proxy.html

+<link rel="import" href="chrome://resources/html/cr.html">
+<script src="plural_string_proxy.js"></script>

chrome/browser/resources/settings/plural_string_proxy.js

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview A helper object used to get a pluralized string.
+ */
+
+cr.define('settings', function() {
+  /** @interface */
+  class PluralStringProxy {
+    /**
+     * Obtains a pluralized string for |messageName| with |itemCount| items.
+     * @param {!string} messageName The name of the message.
+     * @param {!number} itemCount The number of items.
+     * @return {!Promise<string>} Promise resolved with the appropriate plural
+     *     string for |messageName| with |itemCount| items.
+     */
+    getPluralString(messageName, itemCount) {}
+  }
+
+  /** @implements {settings.PluralStringProxy} */
+  class PluralStringProxyImpl {
+    /** @override */
+    getPluralString(messageName, itemCount) {
+      return cr.sendWithPromise('getPluralString', messageName, itemCount);
+    }
+  }
+
+  cr.addSingletonGetter(PluralStringProxyImpl);
+
+  // #cr_define_end
+  return {PluralStringProxy, PluralStringProxyImpl};
+});

chrome/browser/resources/settings/settings_resources.grd

@@ -808,6 +808,12 @@
       <structure name="IDR_SETTINGS_OPEN_WINDOW_PROXY_JS"
                  file="open_window_proxy.js"
                  type="chrome_html" />
+      <structure name="IDR_SETTINGS_PLURAL_STRING_PROXY_HTML"
+                 file="plural_string_proxy.html"
+                 type="chrome_html" />
+      <structure name="IDR_SETTINGS_PLURAL_STRING_PROXY_JS"
+                 file="plural_string_proxy.js"
+                 type="chrome_html" />
       <structure name="IDR_SETTINGS_PAGE_VISIBILITY_HTML"
                  file="page_visibility.html"
                  type="chrome_html" />

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

@@ -26,6 +26,7 @@
 #include "chrome/browser/ui/webui/favicon_source.h"
 #include "chrome/browser/ui/webui/managed_ui_handler.h"
 #include "chrome/browser/ui/webui/metrics_handler.h"
+#include "chrome/browser/ui/webui/plural_string_handler.h"
 #include "chrome/browser/ui/webui/settings/about_handler.h"
 #include "chrome/browser/ui/webui/settings/accessibility_main_handler.h"
 #include "chrome/browser/ui/webui/settings/appearance_handler.h"
@@ -303,6 +304,9 @@ SettingsUI::SettingsUI(content::WebUI* web_ui)
   AddSettingsPageUIHandler(
       base::WrapUnique(ResetSettingsHandler::Create(html_source, profile)));
 
+  // Add a handler to provide pluralized strings.
+  web_ui->AddMessageHandler(std::make_unique<PluralStringHandler>());
+
   // Add the metrics handler to write uma stats.
   web_ui->AddMessageHandler(std::make_unique<MetricsHandler>());