Partial fix for mutable Bitmaps in BitmapShader

This handles the basic case only but unfortunately
a complete solution is too complex to handle just yet

Fixes: 289012318
Test: hwuiunit
Change-Id: I950da9885a40fe623f9cefc202727616fb6ce8b2
diff --git a/libs/hwui/SkiaCanvas.h b/libs/hwui/SkiaCanvas.h
index b785989..ced0224 100644
--- a/libs/hwui/SkiaCanvas.h
+++ b/libs/hwui/SkiaCanvas.h
@@ -175,7 +175,7 @@
                                   const Paint& paint, const SkPath& path, size_t start,
                                   size_t end) override;
 
-    void onFilterPaint(Paint& paint);
+    virtual void onFilterPaint(Paint& paint);
 
     Paint filterPaint(const Paint& src) {
         Paint dst(src);