Set LCD font smoothing to "medium" for gm on Mac, regardless of system settings

http://code.google.com/p/skia/issues/detail?id=382 ('make gm results consistent regardless of system LCDtext settings')
Review URL: https://codereview.appspot.com/5661043

git-svn-id: http://skia.googlecode.com/svn/trunk@3184 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/gmmain.cpp b/gm/gmmain.cpp
index 455f7fe..3958998 100644
--- a/gm/gmmain.cpp
+++ b/gm/gmmain.cpp
@@ -6,6 +6,7 @@
  */
 
 #include "gm.h"
+#include "system_preferences.h"
 #include "GrContext.h"
 #include "GrRenderTarget.h"
 
@@ -654,6 +655,8 @@
     // we don't need to see this during a run
     gSkSuppressFontCachePurgeSpew = true;
 
+    setSystemPreferences();
+
     const char* writePath = NULL;   // if non-null, where we write the originals
     const char* readPath = NULL;    // if non-null, were we read from to compare
     const char* diffPath = NULL;    // if non-null, where we write our diffs (from compare)