Fix language switcher persistence to work when no custom file extension

mappings are set yet - don't leave default value of pref undefined.

Clarify two other cases of definePreference() calls where we really *do*
want the default value to be undefined by passing it explicitly.

Also: add TODOs for unused Session arg in JS code hints.

Author: peterflynn

src/extensibility/Package.js

@@ -41,7 +41,7 @@ define(function (require, exports, module) {
         NodeConnection       = require("utils/NodeConnection"),
         PreferencesManager   = require("preferences/PreferencesManager");
 
-    PreferencesManager.definePreference("proxy", "string");
+    PreferencesManager.definePreference("proxy", "string", undefined);
 
     var Errors = {
         ERROR_LOADING: "ERROR_LOADING",

src/extensions/default/JSLint/main.js

@@ -50,7 +50,7 @@ define(function (require, exports, module) {
      */
     var _lastRunOptions;
 
-    prefs.definePreference("options", "object")
+    prefs.definePreference("options", "object", undefined)
         .on("change", function (e, data) {
             var options = prefs.get("options");
             if (!_.isEqual(options, _lastRunOptions)) {

src/extensions/default/JavaScriptCodeHints/ScopeManager.js

@@ -1036,7 +1036,7 @@ define(function (require, exports, module) {
         /**
          *  Do the work to initialize a code hinting session.
          *
-         * @param {Session} session - the active hinting session
+         * @param {Session} session - the active hinting session (TODO: currently unused)
          * @param {!Document} document - the document the editor has changed to
          * @param {?Document} previousDocument - the document the editor has changed from
          */
@@ -1136,7 +1136,7 @@ define(function (require, exports, module) {
         /**
          * Called each time a new editor becomes active.
          *
-         * @param {Session} session - the active hinting session
+         * @param {Session} session - the active hinting session (TODO: currently unused by doEditorChange())
          * @param {!Document} document - the document of the editor that has changed
          * @param {?Document} previousDocument - the document of the editor is changing from
          */

src/language/LanguageManager.js

@@ -1006,7 +1006,7 @@ define(function (require, exports, module) {
      *     }
      */
     function _updateFromPrefs(pref) {
-        var newMapping = PreferencesManager.get(pref) || {},
+        var newMapping = PreferencesManager.get(pref),
             newNames = Object.keys(newMapping),
             state = _prefState[pref],
             last = state.last,
@@ -1103,14 +1103,14 @@ define(function (require, exports, module) {
         // depends on FileUtils) here. Using the async form of require fixes this.
         require(["preferences/PreferencesManager"], function (pm) {
             PreferencesManager = pm;
-            _updateFromPrefs(_EXTENSION_MAP_PREF);
-            _updateFromPrefs(_NAME_MAP_PREF);
-            pm.definePreference(_EXTENSION_MAP_PREF, "object").on("change", function () {
+            pm.definePreference(_EXTENSION_MAP_PREF, "object", {}).on("change", function () {
                 _updateFromPrefs(_EXTENSION_MAP_PREF);
             });
-            pm.definePreference(_NAME_MAP_PREF, "object").on("change", function () {
+            pm.definePreference(_NAME_MAP_PREF, "object", {}).on("change", function () {
                 _updateFromPrefs(_NAME_MAP_PREF);
             });
+            _updateFromPrefs(_EXTENSION_MAP_PREF);
+            _updateFromPrefs(_NAME_MAP_PREF);
         });
     });