Ensure that we use different glyph entries for regular and df text.

Currently if we switch between regular text and df text while using
the same GrContext, they may use the same entry in the Ganesh font cache,
which is incorrect. This change ensures that they will have different entries.

Committed: https://skia.googlesource.com/skia/+/8dc58edd71c11f232860724dfa3b566895478034

Review URL: https://codereview.chromium.org/1020593003
5 files changed