Add a new transformOrigin field to GraphicsLayer, to replace anchorPoint.

First of several patches.

It is an absolute offset rather than a fraction of layer size. This will
allow us to improve performance slightly on the cc side and remove a hack
in CompositedLayerMapping for zero-sized layers.

TBR=dglazkov@chromium.org
BUG=372837

Review URL: https://codereview.chromium.org/294963006

git-svn-id: svn://svn.chromium.org/blink/trunk@174619 bbb929c8-8fbe-4397-9dbb-9b2b20218538
New Layout Tests to verify grid container's margin don't collapse.

BUG=79180

Review URL: https://codereview.chromium.org/273643008

git-svn-id: svn://svn.chromium.org/blink/trunk@174620 bbb929c8-8fbe-4397-9dbb-9b2b20218538