Enable partial invalidates when rendering with OpenGL.

Change-Id: Ie8be06c4776b815e8737753eb8003b4fd8936130
diff --git a/libs/hwui/LayerRenderer.h b/libs/hwui/LayerRenderer.h
index 1e39847..d2f565e 100644
--- a/libs/hwui/LayerRenderer.h
+++ b/libs/hwui/LayerRenderer.h
@@ -46,7 +46,7 @@
     ~LayerRenderer() {
     }
 
-    void prepare(bool opaque);
+    void prepareDirty(float left, float top, float right, float bottom, bool opaque);
     void finish();
 
     bool hasLayer();