Added the framework for having canvas/recorder/picture record depth_set's.

src/core/SkLightingShader.cpp

Index: src/core/SkLightingShader.cpp
diff --git a/src/core/SkLightingShader.cpp b/src/core/SkLightingShader.cpp
index 473028105a9c5a295b90dd438a43a3c6be0af353..400761d0ce7d4d38a2a7b7d193949961e1d1f45c 100644
--- a/src/core/SkLightingShader.cpp
+++ b/src/core/SkLightingShader.cpp
@@ -134,6 +134,7 @@ 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
             }
         }
 
@@ -176,6 +177,9 @@ 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