Add nested SkPictureImageFilters to the GPU veto.

src/core/SkImageFilter.cpp

Index: src/core/SkImageFilter.cpp
diff --git a/src/core/SkImageFilter.cpp b/src/core/SkImageFilter.cpp
index c7a570121b9a4d96f99244c1f7afa417f8f5cd1d..63f10ad85e3e06e6b7598c568ce6d7bbe6816f73 100644
--- a/src/core/SkImageFilter.cpp
+++ b/src/core/SkImageFilter.cpp
@@ -446,3 +446,13 @@ sk_sp<SkSpecialImage> SkImageFilter::filterInput(int index,
 void SkImageFilter::PurgeCache() {
     SkImageFilterCache::Get()->purge();
 }
+
+int SkImageFilter::numSlowPaths() const {
+    int count = 0;
+    for (int i = 0; i < fInputs.count(); i++) {
+        if (fInputs[i]) {
+            count += fInputs[i]->numSlowPaths();
+        }
+    }
+    return count;
+}