Add SkRuntimeEffect accessor to SkColorFilterBase.

This mirrors the SkRuntimeEffect accessor in SkShaderBase and
SkBlenderBase, and will be used in a followup CL which will allow
hooking up debug traces to runtime effects of any type.

Change-Id: I4449333dac3f2af7b11868d9baf0a82b35ca5aaf
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/478960
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>

src/core/SkColorFilterBase.h

@@ -18,6 +18,7 @@ class GrRecordingContext;
 class SkArenaAlloc;
 class SkBitmap;
 class SkColorSpace;
+class SkRuntimeEffect;
 struct SkStageRec;
 using GrFPResult = std::tuple<bool, std::unique_ptr<GrFragmentProcessor>>;
 
@@ -55,6 +56,8 @@ public:
 
     static void RegisterFlattenables();
 
+    virtual SkRuntimeEffect* asRuntimeEffect() const { return nullptr; }
+
     static SkFlattenable::Type GetFlattenableType() {
         return kSkColorFilter_Type;
     }

src/core/SkRuntimeEffect.cpp

@@ -929,6 +929,8 @@ public:
         write_child_effects(buffer, fChildren);
     }
 
+    SkRuntimeEffect* asRuntimeEffect() const override { return fEffect.get(); }
+
     SK_FLATTENABLE_HOOKS(SkRuntimeColorFilter)
 
 private: