25922 update lint list (cla: yes, team)

25974 Add a validator to ensure NO_PROXY is set correctly if HTTP_PROXY is set (cla: yes, t: flutter doctor, tool)

25977 Add didSendFirstFrameEvent service extension. (cla: yes, framework)

25980 Ensure all errors thrown by image providers can be caught by developers. (cla: yes, framework)

25984 use RRect to draw avatar check on chip (cla: yes, f: material design, framework)

25988 Add Golden test for background painting order. (a: tests, cla: yes, engine)

25992 Add docs to TextStyle for fontFamilyFallback/Custom font fallback (cla: yes, d: api docs, framework)