feat: dropdown add scrollbar

packages/dropdown/src/dropdown-menu.vue

@@ -1,11 +1,17 @@
 <template>
   <transition name="el-zoom-in-top" @after-leave="doDestroy">
-    <ul class="el-dropdown-menu el-popper" :class="[size && `el-dropdown-menu--${size}`]" v-show="showPopper">
-      <slot></slot>
-    </ul>
+    <div class="el-dropdown-menu el-popper" :class="[size && `el-dropdown-menu--${size}`]" v-show="showPopper">
+      <el-scrollbar 
+        tag="ul"
+        wrap-class="dropdown-scrollbar__wrap"
+        view-class="dropdown-scrollbar__list">
+        <slot></slot>
+      </el-scrollbar>
+    </div>
   </transition>
 </template>
 <script>
+  import ElScrollbar from 'element-ui/packages/scrollbar';
   import Popper from 'element-ui/src/utils/vue-popper';
 
   export default {
@@ -13,6 +19,10 @@
 
     componentName: 'ElDropdownMenu',
 
+    components: {
+      ElScrollbar
+    },
+
     mixins: [Popper],
 
     props: {

packages/theme-chalk/src/dropdown.scss

@@ -180,3 +180,11 @@
     }
   }
 }
+
+.dropdown-scrollbar__wrap{
+  max-height: 274px;
+}
+.dropdown-scrollbar__list{
+  padding: 0;
+  margin: 0;
+}