Create new 'skia_os' variable to replace use of 'OS' in most places.
http://codereview.appspot.com/4627085



git-svn-id: http://skia.googlecode.com/svn/trunk@1782 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/SimpleCocoaApp.gyp b/gyp/SimpleCocoaApp.gyp
index 9f415e4..ead9fe4 100644
--- a/gyp/SimpleCocoaApp.gyp
+++ b/gyp/SimpleCocoaApp.gyp
@@ -28,7 +28,7 @@
       ],
       'conditions' : [
         # Only supports Mac currently
-        [ 'OS == "mac"', {
+        [ 'skia_os == "mac"', {
           'sources': [
             '../include/utils/mac/SkCGUtils.h',
             '../src/utils/mac/SkCreateCGImageRef.cpp',