Correctly apply filters to Alpha8 bitmaps.

This change also removes unnecessary operations from display lists.

Change-Id: I627f85861982731f0ee7705b48b36d9c56f22f39
diff --git a/libs/hwui/OpenGLRenderer.h b/libs/hwui/OpenGLRenderer.h
index 7362473..402563c 100644
--- a/libs/hwui/OpenGLRenderer.h
+++ b/libs/hwui/OpenGLRenderer.h
@@ -279,6 +279,8 @@
     void drawShape(float left, float top, const PathTexture* texture, SkPaint* paint);
     void drawRectAsShape(float left, float top, float right, float bottom, SkPaint* p);
 
+    void drawAlphaBitmap(Texture* texture, float left, float top, SkPaint* paint);
+
     /**
      * Draws a textured rectangle with the specified texture. The specified coordinates
      * are transformed by the current snapshot's transform matrix.