feat(facade): add equals method to StringMapWrapper

modules/angular2/src/facade/collection.dart

@@ -86,6 +86,17 @@ class StringMapWrapper {
     return a.keys.toList();
   }
   static bool isEmpty(Map m) => m.isEmpty;
+  static bool equals(Map m1, Map m2) {
+    if (m1.length != m2.length) {
+      return false;
+    }
+    for (var key in m1.keys) {
+      if (m1[key] != m2[key]) {
+        return false;
+      }
+    }
+    return true;
+  }
 }
 
 class ListWrapper {

modules/angular2/src/facade/collection.ts

@@ -86,6 +86,22 @@ export class StringMapWrapper {
 
     return m;
   }
+
+  static equals(m1, m2) {
+    var k1 = Object.keys(m1);
+    var k2 = Object.keys(m2);
+    if (k1.length != k2.length) {
+      return false;
+    }
+    var key;
+    for (var i = 0; i < k1.length; i++) {
+      key = k1[i];
+      if (m1[key] !== m2[key]) {
+        return false;
+      }
+    }
+    return true;
+  }
 }
 
 export class ListWrapper {