remove unecessary lock for two-way props (fix #1067)

Author: yyx990803

src/directives/prop.js

@@ -18,30 +18,14 @@ module.exports = {
     var childKey = prop.path
     var parentKey = prop.parentPath
 
-    // simple lock to avoid circular updates.
-    // without this it would stabilize too, but this makes
-    // sure it doesn't cause other watchers to re-evaluate.
-    var locked = false
-    function withLock (fn) {
-      return function (val) {
-        if (!locked) {
-          locked = true
-          fn(val)
-          _.nextTick(function () {
-            locked = false
-          })
-        }
-      }
-    }
-
     this.parentWatcher = new Watcher(
       parent,
       parentKey,
-      withLock(function (val) {
+      function (val) {
         if (_.assertProp(prop, val)) {
           child[childKey] = val
         }
-      })
+      }
     )
 
     // set the child initial value.
@@ -64,9 +48,9 @@ module.exports = {
         self.childWatcher = new Watcher(
           child,
           childKey,
-          withLock(function (val) {
+          function (val) {
             parent.$set(parentKey, val)
-          })
+          }
         )
       })
     }