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

Review-Url: https://codereview.chromium.org/2391943002
Cr-Commit-Position: refs/heads/master@{#422842}
17 files changed