Add StyleDifference::needsPaintPropertyUpdate() to indicate a style
change directly needs paint property update, and set the flag on
changes of css clip, transform, etc.

Move two tests from their original directory into paint/invalidation.

BUG=645667
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2570463004
Cr-Commit-Position: refs/heads/master@{#438068}