Don't require getLength on Mac.

For consistency with our other image decoders, do not depend on getLength
in Mac specific decoder.

BUG=skia:1570
R=djsollen@google.com

Review URL: https://codereview.chromium.org/23004008

git-svn-id: http://skia.googlecode.com/svn/trunk@10990 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed