72788 [State Restoration] Scaffold.drawer and Scaffold.endDrawer (a: state restoration, cla: yes, f: material design, framework, waiting for tree to go green)

72792 Migrated some services and widgets doc comments to null safety. (cla: yes, framework, team, waiting for tree to go green)

72794 [NNBD] Migrate sample code pt 1 (a: null-safety, cla: yes, f: material design, framework, waiting for tree to go green)

72798 [NNBD] Migrate sample code pt 2 (a: null-safety, cla: yes, f: material design, framework, waiting for tree to go green)

72803 [text_input] prepare for custom text input sources (cla: yes, framework, waiting for tree to go green)