61662 add static method to create material hero controller (cla: yes, f: material design, framework, waiting for tree to go green)

61664 Add minWidth and height parameter into FlatButton widget (cla: yes, f: material design, framework, waiting for tree to go green)

61666 Fix Border.symmetric: phase 2 (cla: yes, framework)

61667 Add tests for platform views’ hover behavior  (a: mouse, a: platform-views, cla: yes, framework)

61668 Track used Android pointer IDs and reuse IDs after a pointer is released (cla: yes, framework, waiting for tree to go green)

61671 Add no-op callbacks to platform view gesture recognizer when necessary (cla: yes, framework)

61672 Remove TODO around deprecation (cla: yes, framework, waiting for tree to go green)