Ensure squashed layers update their offsetFromRenderer when needed.

When some properties of GraphicsLayerPaintInfo change for
a squashed layer (in this case, specifically
GraphicsLayerPaintInfo::offsetFromSquashingCLM), they
don't get properly updated and propagated into the
squashed layer's offsetFromRenderer property in
CompositedLayerMapping::updateGraphicsLayerGeometry().

BUG=336562

Review URL: https://codereview.chromium.org/140583005

git-svn-id: svn://svn.chromium.org/blink/trunk@166339 bbb929c8-8fbe-4397-9dbb-9b2b20218538