Introduce GrColorSpaceXform, for gamut conversion on textures

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"
+
+sk_sp<GrColorSpaceXform> GrColorSpaceXform::Make(SkColorSpace* src,
+                                                               SkColorSpace* dst) {
+    if (!src || !dst) {
+        // Invalid
+        return nullptr;
+    }
+
+    if (src == dst) {
+        // Quick equality check - no conversion needed in this case
+        return nullptr;
+    }
+
+    SkMatrix44 srcToDst(SkMatrix44::kUninitialized_Constructor);
+    if (!dst->xyz().invert(&srcToDst)) {
+        return nullptr;
+    }
+    srcToDst.postConcat(src->xyz());
+
+    return sk_make_sp<GrColorSpaceXform>(srcToDst);
+}