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- Update spec links to the implementation checkpoint
- Use #section-name instead of #rfc.section.numbers as numbers may change.

Bug: 803774
Change-Id: I6f8a72bd89b7deacb33f9da237caa640b86333bd
Reviewed-on: https://chromium-review.googlesource.com/981813Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546045}