Image Filters: refactor all CPU input processing into a filterInput helper function.

gm/imagefiltersgraph.cpp

Index: gm/imagefiltersgraph.cpp
diff --git a/gm/imagefiltersgraph.cpp b/gm/imagefiltersgraph.cpp
index 3ef2a1e589dc6cef561cf932dfceb7a9d26a565e..e27a523cbc6289eec6438a562b237476aca01aa7 100644
--- a/gm/imagefiltersgraph.cpp
+++ b/gm/imagefiltersgraph.cpp
@@ -41,9 +41,8 @@ public:
     virtual bool onFilterImage(Proxy* proxy, const SkBitmap& src, const Context& ctx,
                                SkBitmap* dst, SkIPoint* offset) const override {
         SkBitmap source = src;
-        SkImageFilter* input = getInput(0);
         SkIPoint srcOffset = SkIPoint::Make(0, 0);
-        if (input && !input->filterImage(proxy, src, ctx, &source, &srcOffset)) {
+        if (!this->filterInput(0, proxy, src, ctx, &source, &srcOffset)) {
             return false;
         }