Merge SimpleFontData.cpp and SimpleFontDataSkia.cpp

SimpleFontData.cpp and SimpleFontDataSkia.cpp are now both built on all
platforms thus the separation no longer makes sense. Merge the two into
SimpleFontData.cpp

BUG=356808
R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/212863008

git-svn-id: svn://svn.chromium.org/blink/trunk@183163 bbb929c8-8fbe-4397-9dbb-9b2b20218538