Implement onMakeClone(const SkFontArguments& args) in class SkTypeface_AndroidSystem.

Add FontMgrAndroidSystemVariableTypeface test to test the above
function.

Change-Id: I36a2f65550784a86feecc6ef69a870a33e973804
Reviewed-on: https://skia-review.googlesource.com/136248
Commit-Queue: Bruce Wang <brucewang@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
2 files changed