Fix math issue when transforming text in perspective

Change-Id: Iad6b4e477c11bd1ef5f0ceab2fabcd440030154d
diff --git a/libs/hwui/font/Font.h b/libs/hwui/font/Font.h
index 542b552..b2382f4 100644
--- a/libs/hwui/font/Font.h
+++ b/libs/hwui/font/Font.h
@@ -70,6 +70,7 @@
         float mStrokeWidth;
         bool mAntiAliasing;
         SkMatrix mLookupTransform;
+        SkMatrix mInverseLookupTransform;
     };
 
     ~Font();