move getAdvancedTypefaceMetrics into private, as only skia internals call it

BUG=skia:
R=bungeman@google.com, vandebo@chromium.org

Review URL: https://codereview.chromium.org/148583002

git-svn-id: http://skia.googlecode.com/svn/trunk@13206 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed