adding new GM to demostrate new shadows

src/core/SkLightingShader.cpp

Index: src/core/SkLightingShader.cpp
diff --git a/src/core/SkLightingShader.cpp b/src/core/SkLightingShader.cpp
index f32aa9f411b1f30a93c6f081713f0385c87f1051..c404b39719593f29860964e7dbe512ce16e1402c 100644
--- a/src/core/SkLightingShader.cpp
+++ b/src/core/SkLightingShader.cpp
@@ -164,6 +164,7 @@ public:
                 // TODO: handle more than one of these
                 fLightColor = lights->light(i).color();
                 fLightDir = lights->light(i).dir();
+                // get the handle to the shadow map if there is one
             }
         }
 
@@ -210,6 +211,9 @@ public:
             this->emitChild(0, nullptr, &dstNormalName, args);
 
             fragBuilder->codeAppendf("vec3 normal = %s.xyz;", dstNormalName.c_str());
+
+            // TODO: make this a loop and modulate the contribution from each light
+            // based on the shadow map
             fragBuilder->codeAppendf("float NdotL = clamp(dot(normal, %s), 0.0, 1.0);",
                                      lightDirUniName);
             // diffuse light