use (temp) gpu-imagefilter-cache for applyFilter

src/gpu/SkGpuDevice.h

Index: src/gpu/SkGpuDevice.h
diff --git a/src/gpu/SkGpuDevice.h b/src/gpu/SkGpuDevice.h
index 2e8d14e7a55494f698e66750213445a00b1303b9..b2031e8a229ab517a7e35850c59c2e5f3f826fd3 100644
--- a/src/gpu/SkGpuDevice.h
+++ b/src/gpu/SkGpuDevice.h
@@ -135,6 +135,8 @@ public:
                        const SkImageFilter::Context&,
                        SkBitmap* result, SkIPoint* offset);
 
+    static SkImageFilter::Cache* NewImageFilterCache();
+
 protected:
     bool onReadPixels(const SkImageInfo&, void*, size_t, int, int) override;
     bool onWritePixels(const SkImageInfo&, const void*, size_t, int, int) override;