Update vendor/underscore and add _.indexBy perf and unit tests.

Former-commit-id: 5fc6c853773385aa39d470429899a35f9f17cad8

vendor/underscore/underscore.js

@@ -8,7 +8,7 @@
   // Baseline setup
   // --------------
 
-  // Establish the root object, `window` in the browser, or `global` on the server.
+  // Establish the root object, `window` in the browser, or `exports` on the server.
   var root = this;
 
   // Save the previous value of the `_` variable.
@@ -78,7 +78,7 @@
     if (nativeForEach && obj.forEach === nativeForEach) {
       obj.forEach(iterator, context);
     } else if (obj.length === +obj.length) {
-      for (var i = 0, l = obj.length; i < l; i++) {
+      for (var i = 0, length = obj.length; i < length; i++) {
         if (iterator.call(context, obj[i], i, obj) === breaker) return;
       }
     } else {
@@ -341,6 +341,14 @@
     });
   };
 
+  // Indexes the object's values by a criterion, similar to `groupBy`, but for 
+  // when you know that your index values will be unique.
+  _.indexBy = function(obj, value, context) {
+    return group(obj, value, context, function(result, key, value) {
+      result[key] = value;
+    });
+  };
+
   // Counts instances of an object that group by a certain criterion. Pass
   // either a string attribute to count by, or a function that returns the
   // criterion.
@@ -508,7 +516,7 @@
   _.object = function(list, values) {
     if (list == null) return {};
     var result = {};
-    for (var i = 0, l = list.length; i < l; i++) {
+    for (var i = 0, length = list.length; i < length; i++) {
       if (values) {
         result[list[i]] = values[i];
       } else {
@@ -526,17 +534,17 @@
   // for **isSorted** to use binary search.
   _.indexOf = function(array, item, isSorted) {
     if (array == null) return -1;
-    var i = 0, l = array.length;
+    var i = 0, length = array.length;
     if (isSorted) {
       if (typeof isSorted == 'number') {
-        i = (isSorted < 0 ? Math.max(0, l + isSorted) : isSorted);
+        i = (isSorted < 0 ? Math.max(0, length + isSorted) : isSorted);
       } else {
         i = _.sortedIndex(array, item);
         return array[i] === item ? i : -1;
       }
     }
     if (nativeIndexOf && array.indexOf === nativeIndexOf) return array.indexOf(item, isSorted);
-    for (; i < l; i++) if (array[i] === item) return i;
+    for (; i < length; i++) if (array[i] === item) return i;
     return -1;
   };
 
@@ -562,11 +570,11 @@
     }
     step = arguments[2] || 1;
 
-    var len = Math.max(Math.ceil((stop - start) / step), 0);
+    var length = Math.max(Math.ceil((stop - start) / step), 0);
     var idx = 0;
-    var range = new Array(len);
+    var range = new Array(length);
 
-    while(idx < len) {
+    while(idx < length) {
       range[idx++] = start;
       start += step;
     }
@@ -754,22 +762,33 @@
 
   // Retrieve the values of an object's properties.
   _.values = function(obj) {
-    var values = [];
-    for (var key in obj) if (_.has(obj, key)) values.push(obj[key]);
+    var keys = _.keys(obj);
+    var length = keys.length;
+    var values = new Array(length);
+    for (var i = 0; i < length; i++) {
+      values[i] = obj[keys[i]];
+    }
     return values;
   };
 
   // Convert an object into a list of `[key, value]` pairs.
   _.pairs = function(obj) {
-    var pairs = [];
-    for (var key in obj) if (_.has(obj, key)) pairs.push([key, obj[key]]);
+    var keys = _.keys(obj);
+    var length = keys.length;
+    var pairs = new Array(length);
+    for (var i = 0; i < length; i++) {
+      pairs[i] = [keys[i], obj[keys[i]]];
+    }
     return pairs;
   };
 
   // Invert the keys and values of an object. The values must be serializable.
   _.invert = function(obj) {
     var result = {};
-    for (var key in obj) if (_.has(obj, key)) result[obj[key]] = key;
+    var keys = _.keys(obj);
+    for (var i = 0, length = keys.length; i < length; i++) {
+      result[obj[keys[i]]] = keys[i];
+    }
     return result;
   };
 
@@ -1053,8 +1072,7 @@
       '<': '&lt;',
       '>': '&gt;',
       '"': '&quot;',
-      "'": '&#x27;',
-      '/': '&#x2F;'
+      "'": '&#x27;'
     }
   };
   entityMap.unescape = _.invert(entityMap.escape);
@@ -1085,7 +1103,7 @@
 
   // Add your own custom functions to the Underscore object.
   _.mixin = function(obj) {
-    each(_.functions(obj), function(name){
+    each(_.functions(obj), function(name) {
       var func = _[name] = obj[name];
       _.prototype[name] = function() {
         var args = [this._wrapped];