Enforce comment formatting in platform/

Like https://codereview.chromium.org/2394883002/ but for platform.

Also rewrap a few last comments that landed in the last day,
and reformat platform.

BUG=563793
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2394853003
Cr-Commit-Position: refs/heads/master@{#423318}
7 files changed