7374 Revert “Test SDK roll” (cla: yes)

7387 Improve TextAffinity Docs (cla: yes)

7398 Replace Java code with equivalent, more concise code. (cla: yes)

7401 Reset ParagraphBuilder after build() (cla: yes)

7403 Dart SDK roll for 2019-01-07 (cla: yes)

7404 fix up analysis for Dart in Engine (cla: yes)

7405 Dart SDK roll for 2019-01-07 (cla: yes)

7409 Cleanup dead code (cla: yes)

7410 Refactor shared code into separate function to simplify further work. (cla: yes)