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More details:
- Injecting std::cout and std::cerr into Main*() functions.
- Add MainParams to simplify interfaces of Main*() functions.
- Add skeletal file reads and dummy file write to Zucchini-gen and
  Zucchini-apply.

Bug: 729154
Change-Id: I35d11e99b1863e77dee084635589022a6862d6e8
Reviewed-on: https://chromium-review.googlesource.com/592053
Commit-Queue: Samuel Huang <huangs@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490807}