50663 add an –enable-observatory flag (cla: yes, tool, waiting for tree to go green)

50664 Made xcode_backend stop on error. (cla: yes, tool, waiting for tree to go green)

50666 update packages (cla: yes, team, waiting for tree to go green)

50669 [flutter_tools] Disable analytics on more bots (cla: yes, tool, waiting for tree to go green)

50670 Expose showButtonMenu of PopupMenuButtonState (cla: yes, f: material design, framework, waiting for tree to go green)

50671 Roll engine 0e8ed2715a35..e0ebaea59071 (31 commits) (cla: yes, waiting for tree to go green)