Convert child FPs from refs to pending executions when parent converts

Review URL: https://codereview.chromium.org/1315923004
diff --git a/include/gpu/GrFragmentProcessor.h b/include/gpu/GrFragmentProcessor.h
index e4d9151..9c9f05a 100644
--- a/include/gpu/GrFragmentProcessor.h
+++ b/include/gpu/GrFragmentProcessor.h
@@ -126,6 +126,8 @@
     virtual void onComputeInvariantOutput(GrInvariantOutput* inout) const = 0;
 
 private:
+    void notifyRefCntIsZero() const final;
+
     /** Returns a new instance of the appropriate *GL* implementation class
         for the given GrFragmentProcessor; caller is responsible for deleting
         the object. */