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/gyp@10990 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/images.gyp b/images.gyp
index 7abaac2..7ead87e 100644
--- a/images.gyp
+++ b/images.gyp
@@ -22,6 +22,8 @@
         '../src/core/',
         # for access to SkImagePriv.h
         '../src/image/',
+        # So src/ports/SkImageDecoder_CG can access SkStreamHelpers.h
+        '../src/images/',
       ],
       'sources': [
         '../include/images/SkForceLinking.h',