62330 Use a LinkedList to improve the performances of ChangeNotifier (cla: yes, framework)

62337 [Material] Add support for high contrast theming to Material apps (cla: yes, f: material design, framework, waiting for tree to go green)

62338 Replace mistaken dartdoc [Foo..bar] references with [Foo.bar] (cla: yes, f: material design, framework, waiting for tree to go green)

62350 Added OverflowBar widget (cla: yes, framework, waiting for tree to go green)

62359 Fix SemanticsNode.rect position for nested scrollables with useTwoPan… (a: accessibility, cla: yes, f: scrolling, framework, waiting for tree to go green)

62362 Move key event and semantics related method from WidgetTester to WidgetController (a: tests, cla: yes, framework, waiting for tree to go green)