Don't use a magic value for 'auto' oriented <marker>s

The value -1 (degrees) is a valid angle, so using it to indicate that
'auto' orientation should be used does not work out.
Just check 'orientType' directly instead and simplify the angle getter.

BUG=606345

Review URL: https://codereview.chromium.org/1916173003

Cr-Commit-Position: refs/heads/master@{#390029}
4 files changed