[i18n] use Polymer data binding to change locale strings

ui/webui/resources/js/i18n_behavior.js

Index: ui/webui/resources/js/i18n_behavior.js
diff --git a/ui/webui/resources/js/i18n_behavior.js b/ui/webui/resources/js/i18n_behavior.js
index 05c9cf6567893662be14784bc12903e22dd967e6..9c1918f70f4054d6defc8c47b357dafbce1e180a 100644
--- a/ui/webui/resources/js/i18n_behavior.js
+++ b/ui/webui/resources/js/i18n_behavior.js
@@ -4,17 +4,23 @@
 
 /**
  * @fileoverview
- * 'I18nBehavior' is a behavior to mix in loading of
- * internationalization strings.
- *
- * Example:
- *   behaviors: [
- *     I18nBehavior,
- *   ],
+ * 'I18nBehavior' is a behavior to mix in loading of internationalization
+ * strings.
  */
 
 /** @polymerBehavior */
 var I18nBehavior = {
+  properties: {
+    /**
+     * The language the UI is presented in. Used to signal dynamic language
+     * change.
+     */
+    locale: {
+      type: String,
+      value: '',
+    },
+  },
+
   /**
    * Returns a translated string where $1 to $9 are replaced by the given
    * values.
@@ -60,6 +66,19 @@ var I18nBehavior = {
   },
 
   /**
+   * Similar to 'i18n', with an unused |locale| parameter used to trigger
+   * updates when |this.locale| changes.
+   * @param {string} locale The UI language used.
+   * @param {string} id The ID of the string to translate.
+   * @param {...string} var_args Values to replace the placeholders $1 to $9
+   *     in the string.
+   * @return {string} A translated, sanitized, substituted string.
+   */
+  i18nDynamic: function(language, id, var_args) {
+    return this.i18n.apply(this, Array.prototype.slice.call(arguments, 1));

[Dan Beam, 2017/05/22 23:39:02]

i think this slice here is fine

[dschuyler, 2017/05/23 00:03:19]

Acknowledged.

+  },
+
+  /**
    * Returns true if a translation exists for |id|.
    * @param {string} id
    * @return {boolean}
@@ -67,6 +86,15 @@ var I18nBehavior = {
   i18nExists: function(id) {
     return loadTimeData.valueExists(id);
   },
+
+  /**
+   * Call this when UI strings may have changed (e.g. because the locale
+   * changed). This will send an update to any data bindings to
+   * i18nDynamic(locale, ...).
+   */
+  updateLocalizedContent: function() {
+    this.locale = loadTimeData.getString('language');
+  },
 };
 
 /**