Add dithering to gradients

Change-Id: Ic1208855bde3a254eca2fd7cef43e0f1318ce419
diff --git a/libs/hwui/Caches.cpp b/libs/hwui/Caches.cpp
index 258ced0..aa2bc3f 100644
--- a/libs/hwui/Caches.cpp
+++ b/libs/hwui/Caches.cpp
@@ -252,6 +252,7 @@
             dropShadowCache.clear();
             gradientCache.clear();
             fontRenderer->clear();
+            dither.clear();
             // fall through
         case kFlushMode_Moderate:
             fontRenderer->flush();