Refactored SkColorSpace and added in a Lab PCS GM

src/gpu/GrColorSpaceXform.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrColorSpaceXform.h"
 #include "SkColorSpace.h"
 #include "SkColorSpace_Base.h"
@@ skipping 31 matching lines @@
     if (!src || !dst) {
         // Invalid
         return nullptr;
     }
 
     if (src == dst) {
         // Quick equality check - no conversion needed in this case
         return nullptr;
     }
 
+    
+    const SkMatrix44* toXYZD50   = as_CSB(src)->toXYZD50();
+    const SkMatrix44* fromXYZD50 = as_CSB(dst)->fromXYZD50();
+    if (!toXYZD50 || !fromXYZD50) {
+        // unsupported colour spaces -- cannot specify gamut as a matrix
+        return nullptr;
+    }
     SkMatrix44 srcToDst(SkMatrix44::kUninitialized_Constructor);
-    srcToDst.setConcat(as_CSB(dst)->fromXYZD50(), as_CSB(src)->toXYZD50());
+    srcToDst.setConcat(*fromXYZD50, *toXYZD50);
 
     if (matrix_is_almost_identity(srcToDst)) {
         return nullptr;
     }
 
     return sk_make_sp<GrColorSpaceXform>(srcToDst);
 }
 
 bool GrColorSpaceXform::Equals(const GrColorSpaceXform* a, const GrColorSpaceXform* b) {
     if (a == b) {
         return true;
     }
 
     if (!a || !b) {
         return false;
     }
 
     return a->fSrcToDst == b->fSrcToDst;
 }
 
 GrColor4f GrColorSpaceXform::apply(const GrColor4f& srcColor) {
     GrColor4f result;
     fSrcToDst.mapScalars(srcColor.fRGBA, result.fRGBA);
     return result;
 }