更换主窗口菜单项action_mi_gallery的图标资源，修改为原有图标的透明背景方式的图标。

gallery/src/main/res/drawable/ic_mi_gallery3.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android"
+    android:clickable="true">
+    <item 
+        android:left="0dp" 
+        android:top="0dp" 
+        android:right="0dp" 
+        android:bottom="0dp"
+        android:drawable="@drawable/mi_blankbackground"/>
+</layer-list>

gallery/src/main/res/menu/menu_main.xml

@@ -5,7 +5,7 @@
     <item
         android:id="@+id/action_mi_gallery"
         android:title="@string/mi_gallery"
-        android:icon="@drawable/ic_mi_gallery2"
+        android:icon="@drawable/ic_mi_gallery3"
         app:showAsAction="ifRoom"/>
     
     <item