Move vertex buffer setup out of drawPackedGlyph().

This gets a very welcome ~10% speedup on my Mac.

Committed: https://skia.googlesource.com/skia/+/1d38619389cc1100bd516b9acbf17b7bd42d33ce

R=bsalomon@google.com

Author: jvanverth@google.com

Review URL: https://codereview.chromium.org/414573002
5 files changed