Refactoring of GPU NormalMap handling out into its own class

src/core/SkLightingShader.h

Index: src/core/SkLightingShader.h
diff --git a/src/core/SkLightingShader.h b/src/core/SkLightingShader.h
index f25b30342a70699506cc03a5ffbc786e1e620207..c2b65472b924f35d5d757ca751d1aae6fdf0b9ed 100644
--- a/src/core/SkLightingShader.h
+++ b/src/core/SkLightingShader.h
@@ -16,6 +16,55 @@ class SkMatrix;
 
 class SK_API SkLightingShader {
 public:
+    /** Abstract class that generates or reads in normals for use by SkLightingShader. Currently
+        implements the GPU side only. Not to be used as part of the API yet. Used internally by
+        SkLightingShader.
+    */
+    class SK_API NormalSource : public SkFlattenable {
+    public:
+        virtual ~NormalSource();
+
+#if SK_SUPPORT_GPU
+        /** Returns a fragment processor that takes no input and outputs a normal (already rotated)
+            as its output color. To be used as a child fragment processor.
+        */
+        virtual sk_sp<GrFragmentProcessor> asFragmentProcessor(
+                GrContext* context,
+                const SkMatrix& viewM,
+                const SkMatrix* localMatrix,
+                SkFilterQuality filterQuality,
+                SkSourceGammaTreatment gammaTreatment) const = 0;
+#endif
+
+        /** Returns a normal source that provides normals sourced from the the normal map argument.
+              Not to be used as part of the API yet. Used internally by SkLightingShader.
+
+              @param  normal                the normal map
+              @param  invNormRotation       rotation applied to the normal map's normals
+              @param  normLocalM            the local matrix for the normal map
+
+              nullptr will be returned if
+                  'normal' is empty
+                  'normal' too big (> 65535 on either side)
+
+              The normal map is currently assumed to be an 8888 image where the normal at a texel
+              is retrieved by:
+                  N.x = R-127;
+                  N.y = G-127;
+                  N.z = B-127;
+                  N.normalize();
+              The +Z axis is thus encoded in RGB as (127, 127, 255) while the -Z axis is
+              (127, 127, 0).
+        */
+        static sk_sp<NormalSource> MakeMap(const SkBitmap& normal, const SkVector& invNormRotation,
+                                           const SkMatrix* normLocalM);
+
+        SK_DEFINE_FLATTENABLE_TYPE(NormalSource)
+        SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
+    };
+
+
+
     /** Returns a shader that lights the diffuse and normal maps with a set of lights.
 
         It returns a shader with a reference count of 1.