Remove layout-related dirty bit setting in RenderObject::styleWillChange

This also makes more clear why the remaining call to paintInvalidationForWholeRenderer is there (because it's
a style update that does not cause layout).

BUG=

Review URL: https://codereview.chromium.org/386443002

git-svn-id: svn://svn.chromium.org/blink/trunk@177986 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fixes for re-enabling more MSVC level 4 warnings: Source/core/rendering/ edition

This contains fixes for the following sorts of issues:
* Assignment inside conditional
* Possibly-uninitialized local variable

BUG=81439
TEST=none
R=fmalita@chromium.org

Review URL: https://codereview.chromium.org/386043003

git-svn-id: svn://svn.chromium.org/blink/trunk@177987 bbb929c8-8fbe-4397-9dbb-9b2b20218538