[common] Introduce |Size::GetArea()| and comparison operators.
[evita] gfx: Introduce |gfx::SizeF::GetArea()| and comparison operators.
[evita] ui: Revise |ui::Widget::SetBounds()|.
[evita] views: Revise tile animation
[evita] ui: Introduce |ui::AnimationFrameHandler| with |ui::AnimationScheduler| classes.
[evita] views: Introduce |views::ContentObserver| and utilzie |ui::AnimationFrameHandler|.