change measureText impl to first convert to glyphs

Bug: skia:
Change-Id: Icbc53688fb4e575695abf062dfe89e3b4b3bbb53
Reviewed-on: https://skia-review.googlesource.com/c/188021
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed