Enable partial invalidates when rendering with OpenGL.

Change-Id: Ie8be06c4776b815e8737753eb8003b4fd8936130
diff --git a/libs/hwui/OpenGLRenderer.h b/libs/hwui/OpenGLRenderer.h
index bd29609..77de1d2 100644
--- a/libs/hwui/OpenGLRenderer.h
+++ b/libs/hwui/OpenGLRenderer.h
@@ -62,7 +62,8 @@
 
     virtual void setViewport(int width, int height);
 
-    virtual void prepare(bool opaque);
+    void prepare(bool opaque);
+    virtual void prepareDirty(float left, float top, float right, float bottom, bool opaque);
     virtual void finish();
 
     // These two calls must not be recorded in display lists