Use updated signature for decode in empty decoder.

This allows chromium to build SkImageDecoder_empty.cpp
(https://codereview.chromium.org/15960015/) until Skia
has https://codereview.chromium.org/15806010/ (which
is a superset of this change).

R=robertphillips@google.com

Review URL: https://codereview.chromium.org/15742029

git-svn-id: http://skia.googlecode.com/svn/trunk@9321 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed