Rewrap comments to 80 columns in platform/graphics/{compositing,cpu,gpu,skia}/.
This also makes some minor modifications (small rewrites for grammar, etc.).
BUG=
563793
TEST=none
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Committed:
https://crrev.com/742cd0347b9999467d82e6f8a28a7d3b5673c19d
Cr-Commit-Position: refs/heads/master@{#422842}