This directory contains code needed for rendering and interacting with frame decorations in mash.
Immersive fullscreen is a specialized fullscreen mode. In it the user can move the mouse to the top of the screen and the window header will slide down on top of the fullscreen window contents.
There are two distinct ways for immersive mode to work in mash:
Mash handles it all. This is the default. In this mode a separate ui::Window is created for the reveal of the title area. HeaderView is used to render the title area of the reveal in the separate window. The client does nothing special here.
The client takes control of it all (as happens in chrome). To enable this the client sets kDisableImmersive_InitProperty on the window. In this mode the client creates a separate window for the reveal (similar to 1). The reveal window is a child of the window going into immersive mode. Mash knows to paint window decorations to the reveal window by way of the property kRenderParentTitleArea_Property set on the parent window. The client runs all the immersive logic, including positioning of the reveal window.
In both cases DetachedTitleAreaRenderer and HeaderView is used to render the title area. The difference is in the first case mash creates the window, in the second case the child does (and tells mash about it). And of course in the second case the client runs all the immersive logic.