27296 [web] Librarify all remaining files (cla: yes, platform-web, needs tests)

27298 Roll Dart SDK from 83a559e0a9bd to ab8bac9fd542 (1 revision) (cla: yes, waiting for tree to go green)

27299 [web] delete e2etests and all related tooling (cla: yes, platform-web)

27300 Roll Dart SDK from ab8bac9fd542 to 812bf07cf737 (1 revision) (cla: yes, waiting for tree to go green)

27301 Fix duplicated keys with CONTROL key toggled (cla: yes, waiting for tree to go green, platform-windows)

27302 Build rules for scenario_app (cla: yes)