add default arg so android can bulid

Bug: skia:
Change-Id: I2bb10edba9a39f20691398a2a0a01b1da2709fcd
Reviewed-on: https://skia-review.googlesource.com/17761
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed