Naming of boxDecorations

We used the term "boxDecorations" for the following two different
things at different places of rendering code:

- Box decorations that are painted as background (at
  PaintPhaseBlockBackground or PaintPhaseChildBlockBackground):
  This includes borders, shadows, background-colors, background-images
  and any background drawn for any appearence;

- Box decorations drawn around the edges of the box:
  This includes borders, shadows, outlines, any other box decorations
  drawn for appearance, etc. (from RenderLayer.cpp and
  CompositingLayerMapping.cpp)

To make it clear, the term used in the former case is renamed to
'boxDecorationBackground', and the latter case is kept unchanged.

By the way, added RenderStyle::hasBoxDecorations() to avoid
duplicate/inconsistent code, and I'd also like to use the function
in another change that requires the same concept.

Review URL: https://codereview.chromium.org/352423002

git-svn-id: svn://svn.chromium.org/blink/trunk@177253 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Assert the SVG paint invalidation container didn't change in invaliadateTreeAfterLayout

We don't support accelerated layers in SVG yet, so assert that the paint
invalidation container didn't change and avoid doing extra work to prove
that point in SVG's invalidateTreeAfterLayout method.

Review URL: https://codereview.chromium.org/361753004

git-svn-id: svn://svn.chromium.org/blink/trunk@177254 bbb929c8-8fbe-4397-9dbb-9b2b20218538