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- Use a mapping between runtime feature and command line switch
  to control the enable/disable logic for cleaner code

Design docs: https://docs.google.com/document/d/1d6_NBVPXh7B2XMk3H9b_qIxeuSXq6MblVSJldN7bTBY/edit?usp=sharing

Bug: 832393
Change-Id: I67c944e1d20d5c0d9ab871f87641cb6ea46fb8ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1822864
Commit-Queue: Rodney Ding <rodneyding@google.com>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Jason Chase <chasej@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705952}