Fix repaint in sub-pixel composited layers

Prior to properly accumulating sub-pixel offsets through composited layers,
there was a hack in RenderLayerRepainter to adjust repaint rects by the
sub-pixel accumulation. Now that this accumulation is properly handled in
the rest of the stack, this is no longer needed, and instead results in us
applying the sub-pixel offset twice (we'll do it again at paint-time).

BUG=362938

Review URL: https://codereview.chromium.org/244523006

git-svn-id: svn://svn.chromium.org/blink/trunk@172086 bbb929c8-8fbe-4397-9dbb-9b2b20218538