42254 Update minimum version to Xcode 10.2 (cla: yes, tool)

42257 Make Pub an interface in the flutter tool (cla: yes, tool)

42260 Small cleanup of web code (cla: yes, tool)

42267 Improve documentation around animations. (cla: yes, framework, waiting for tree to go green)

42276 Revert removal of linux from unpack command. (cla: yes, tool)

42278 Re-land keyboard traversal PRs (cla: yes, f: cupertino, f: material design, framework, team)

42289 Ensure precache web works on dev branch (cla: yes, tool)

42306 Ensure that flutter assets are copied in the AAR (cla: yes, team, tool, waiting for tree to go green)