adding new GM to demostrate new shadows

include/core/SkLights.h

Index: include/core/SkLights.h
diff --git a/include/core/SkLights.h b/include/core/SkLights.h
index c5c54276a39597909ff53a0465a6e97fee5a8743..01ffddf8bc3d327631a3d0109e173d05a32af567 100644
--- a/include/core/SkLights.h
+++ b/include/core/SkLights.h
@@ -12,6 +12,7 @@
 #include "SkPoint3.h"
 #include "SkRefCnt.h"
 #include "../private/SkTDArray.h"
+#include "SkImage.h"
 
 class SK_API SkLights  : public SkRefCnt {
 public:
@@ -44,11 +45,17 @@ public:
             return fDirection; 
         }
 
+        void setShadowMap(sk_sp<SkImage> shadowMap) {
+            // fShadowMap = shadowMap;
+        }
+
     private:
         LightType   fType;
         SkColor3f   fColor;           // linear (unpremul) color. Range is 0..1 in each channel.
         SkVector3   fDirection;       // direction towards the light (+Z is out of the screen).
                                       // If degenerate, it will be replaced with (0, 0, 1).
+
+        // sk_sp<SkImage> fShadowMap;
     };
 
     class Builder {
@@ -73,7 +80,7 @@ public:
         return fLights.count();
     }
 
-    const Light& light(int index) const {
+    Light& light(int index) {
         return fLights[index];
     }