51518 re-land “Retry cURL downloads” (cla: yes)

51519 Add Linux and Windows target platforms (a: desktop, cla: yes, d: examples, f: cupertino, f: material design, framework, team, team: gallery)

51520 Generate a makefile for Linux plugins (cla: yes, tool)

51523 Roll engine ecabc1037652..060a7733a654 (2 commits) (cla: yes, waiting for tree to go green)

51524 Turn off reupload_on_changes for Cirrus caches (cla: yes, team, team: infra)

51525 Pass RouteSettings into all callers of showGeneralDialog. (cla: yes, f: cupertino, f: material design, framework, waiting for tree to go green)