Replaced calls to LayoutObject.Style() with LayoutObject.StyleRef().

Especially within paint, most calls to LayoutObject.Style() are assuming a non-null pointer and
dereferencing it. To better document the fact that these calls (properly, in most cases)
assume the layout object contains style, they should be replaced with calls to the StyleRef()
function, which dereferences the pointer.

Bug: 872508
Change-Id: Id6a04871c12a2c09d1029ca5aa04ae49099f7fd0
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Reviewed-on: https://chromium-review.googlesource.com/1171144
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Mason Freed <masonfreed@google.com>
Cr-Commit-Position: refs/heads/master@{#582380}
29 files changed