Android App 启动 Activity 创建解析

继承实现类关系：

　　ActivityThread  thread = new ActivityThread();

　　Context->ContextImpl   ContextImpl context = new ContextImpl(null, mainThread, packageInfo, activityInfo.splitName,activityToken, null, 0, classLoader);

 　   Window->PhoneWindow

　　WindowManger->WindowMangerImpl

　　FrameLayout->DecorView

　　ViewRoot->ViewRootImpl