feat(facade): add maximum method for ListWrapper

modules/angular2/src/facade/collection.dart

@@ -217,6 +217,27 @@ class ListWrapper {
     if (end == null) return len;
     return end < 0 ? max(len + end, 0) : min(end, len);
   }
+
+
+  static maximum(List l, fn(item)) {
+    if (l.length == 0) {
+      return null;
+    }
+    var solution = null;
+    var maxValue = double.NEGATIVE_INFINITY;
+    for (var index = 0; index < l.length; index++) {
+      var candidate = l[index];
+      if (candidate == null) {
+        continue;
+      }
+      var candidateValue = fn(candidate);
+      if (candidateValue > maxValue) {
+        solution = candidate;
+        maxValue = candidateValue;
+      }
+    }
+    return solution;
+  }
 }
 
 bool isListLikeIterable(obj) => obj is Iterable;

modules/angular2/src/facade/collection.ts

@@ -1,4 +1,4 @@
-import {isJsObject, global, isPresent, isArray} from 'angular2/src/facade/lang';
+import {isJsObject, global, isPresent, isBlank, isArray} from 'angular2/src/facade/lang';
 
 export var List = global.Array;
 export var Map = global.Map;
@@ -266,6 +266,26 @@ export class ListWrapper {
   }
   static toString<T>(l: List<T>): string { return l.toString(); }
   static toJSON<T>(l: List<T>): string { return JSON.stringify(l); }
+
+  static maximum<T>(list: List<T>, predicate: (T) => number): T {
+    if (list.length == 0) {
+      return null;
+    }
+    var solution = null;
+    var maxValue = -Infinity;
+    for (var index = 0; index < list.length; index++) {
+      var candidate = list[index];
+      if (isBlank(candidate)) {
+        continue;
+      }
+      var candidateValue = predicate(candidate);
+      if (candidateValue > maxValue) {
+        solution = candidate;
+        maxValue = candidateValue;
+      }
+    }
+    return solution;
+  }
 }
 
 export function isListLikeIterable(obj: any): boolean {

modules/angular2/test/facade/collection_spec.ts

@@ -76,6 +76,20 @@ export function main() {
       it('should respect the startIndex parameter',
          () => { expect(ListWrapper.indexOf(l, 1, 1)).toEqual(-1); });
     });
+
+    describe('maximum', () => {
+      it('should return the maximal element',
+         () => { expect(ListWrapper.maximum([1, 2, 3, 4], x => x)).toEqual(4); });
+
+      it('should ignore null values',
+         () => { expect(ListWrapper.maximum([null, 2, 3, null], x => x)).toEqual(3); });
+
+      it('should use the provided function to determine maximum',
+         () => { expect(ListWrapper.maximum([1, 2, 3, 4], x => -x)).toEqual(1); });
+
+      it('should return null for an empty list',
+         () => { expect(ListWrapper.maximum([], x => x)).toEqual(null); });
+    });
   });
 
   describe('StringMapWrapper', () => {