Re-instate geometry sharing optimization for 'd' on <use>'d <path>s

This adds back the geometry sharing optimization initially added in
https://codereview.chromium.org/1425913004 and removed by
https://codereview.chromium.org/1439793003.
This CL moves the optimization from asPath() to
collectStyleForPresentationAttribute(), meaning the optimization only
applies to the presentation attribute style (which is equivalent to
the old version.)

BUG=535429

Review URL: https://codereview.chromium.org/1578363007

Cr-Commit-Position: refs/heads/master@{#369473}
2 files changed