[build] Get rid of "/fp:fast" since Chromium defaults to "/fp:precise".
[evita] views/tabs: Support tab drag and drop.
[evita] views: Move tab related files to "evita/views/tabs/" from "evita/views/".
[evita] views/tab: Rename |TabOwner| to |TabController|.
[evita] ui: Make drop tab not to cause crash.
[evita] gfx: Make |gfx::Canvas::AddDirtyRect()| to handle empty dirty rectangle.