Add SK_API to base classes of classes with SK_API.
https://codereview.appspot.com/6683044/

This change should unblock rolling Skia DEPS past r5914.
TBR=reed


git-svn-id: http://skia.googlecode.com/svn/trunk@5946 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed