MD Settings: Allow the user to order the list of languages.

chrome/browser/resources/settings/languages_page/languages.js

Index: chrome/browser/resources/settings/languages_page/languages.js
diff --git a/chrome/browser/resources/settings/languages_page/languages.js b/chrome/browser/resources/settings/languages_page/languages.js
index 810281f90f6567edef9bc8819734cc903a22709f..700d084dd835635eba85a19d05afff683505766d 100644
--- a/chrome/browser/resources/settings/languages_page/languages.js
+++ b/chrome/browser/resources/settings/languages_page/languages.js
@@ -546,6 +546,29 @@ SettingsLanguagesSingletonElement = Polymer({
   },
 
   /**
+   * Moves the language in the list of enabled languages by the given offset.
+   * @param {string} languageCode
+   * @param {number} offset Negative offset moves the language toward the front
+   *     of the list. A Positive one moves the language toward the back.
+   */
+  moveLanguage: function(languageCode, offset) {
+    if (!CrSettingsPrefs.isInitialized)
+      return;
+
+    var languageCodes =
+        this.getPref(preferredLanguagesPrefName).value.split(',');
+
+    var originalIndex = languageCodes.indexOf(languageCode);
+    var newIndex = originalIndex + offset;
+    if (originalIndex == -1 || newIndex < 0 || newIndex >= languageCodes.length)
+      return;
+
+    languageCodes.splice(originalIndex, 1);
+    languageCodes.splice(newIndex, 0, languageCode);
+    this.languageSettingsPrivate.setLanguageList(languageCodes);

[michaelpg, 2016/06/21 00:34:42]

there's a bug(?) here:
https://cs.chromium.org/chromium/src/components/translate/core/browser/transl...

which will turn this:
  ['en-US', 'es', 'en']
into this:
  ['en-US', 'en', 'es']
(which seems like undesired behavior, thus a bug)

test this by having these languages enabled:
  * English (United States
  * English
  * Spanish

and trying to move Spanish up one.

apparently, old Options doesn't quite update until you refresh the page, so
reordering *seems* to work but doesn't (try it).

in Settings, the result is that nothing happens (we never get a notification
from prefs, because the pref doesn't change). for some reason, we aren't closing
the menu unless we re-create the list (because the items change), so the effect
is that nothing happens and the menu stays open.

do you agree the old Options behavior is buggy? seems like something we should
address in a separate CL, but it makes for a weird bug in Settings.

[Moe, 2016/06/21 20:10:19]

I confirm this behavior. We may need to keep expanding the language codes after
all though. Is it possible to show the cros preferred languages pref as the list
of languages on desktop too? that one get saved without modification.

+  },
+
+  /**
    * Enables translate for the given language by removing the translate
    * language from the blocked languages preference.
    * @param {string} languageCode