Rewrap comments to 80 columns in Source/platform/graphics/paint/.

This also makes some minor modifications (rewrite for clarity, etc.).

BUG=563793
TEST=none
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2385123003
Cr-Commit-Position: refs/heads/master@{#423031}
22 files changed