allow gamma params to be changed in .gyp



git-svn-id: http://skia.googlecode.com/svn/trunk@3294 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/ports/SkFontHost_FreeType.cpp b/src/ports/SkFontHost_FreeType.cpp
index 43b9312..39d6a08 100644
--- a/src/ports/SkFontHost_FreeType.cpp
+++ b/src/ports/SkFontHost_FreeType.cpp
@@ -55,8 +55,13 @@
 //#define DUMP_STRIKE_CREATION
 
 //#define SK_GAMMA_APPLY_TO_A8
-#define SK_GAMMA_CONTRAST   0x66
-#define SK_GAMMA_EXPONENT   2.2
+
+#ifndef SK_GAMMA_CONTRAST
+    #define SK_GAMMA_CONTRAST   0x66
+#endif
+#ifndef SK_GAMMA_EXPONENT
+    #define SK_GAMMA_EXPONENT   2.2
+#endif
 
 #ifdef SK_DEBUG
     #define SkASSERT_CONTINUE(pred)                                                         \