call onGetUPEM to subclasses can optimize it, and place default behavior
(calling getAdvancedTypefaceMetrics) in base impl.

This allows us to remove SkFontHost::GetUnitsPerEm entirely
Review URL: https://codereview.chromium.org/12915003

git-svn-id: http://skia.googlecode.com/svn/trunk@8295 2bbb7eff-a529-9590-31e7-b0007b416f81
4 files changed