61392 Update Card example and shadowColor default (cla: yes, f: material design, framework, waiting for tree to go green)

61394 Update the Scaffold examples; use the new button classes (cla: yes, f: material design, framework)

61398 Prevent material switch from recreating its render object when it becomes disabled (cla: yes, f: material design, framework, waiting for tree to go green)

61401 Make scrollbar thickness and radius customizable (cla: yes, f: cupertino, f: material design, framework)

61424 Update documentation (cla: yes, f: material design, framework)

61439 Add per thumb Range Slider semantics (cla: yes, f: material design, framework, waiting for tree to go green)

61479 Update MaterialState API docs (cla: yes, f: material design, framework, waiting for tree to go green)