Introduce GrColorSpaceXform, for gamut conversion on textures

src/gpu/glsl/GrGLSLColorSpaceXformHelper.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrGLSLColorSpaceXformHelper_DEFINED
+#define GrGLSLColorSpaceXformHelper_DEFINED
+
+#include "GrGLSLUniformHandler.h"
+
+class GrColorSpaceXform;
+
+/**
+ * Stack helper class to assist with using GrColorSpaceXform within an FP's emitCode function.
+ */
+class GrGLSLColorSpaceXformHelper : public SkNoncopyable {
+public:
+    GrGLSLColorSpaceXformHelper(GrGLSLUniformHandler* uniformHandler,
+                                GrColorSpaceXform* colorSpaceXform,
+                                GrGLSLProgramDataManager::UniformHandle* handle) {
+        SkASSERT(uniformHandler && handle);
+        if (colorSpaceXform) {
+            *handle = uniformHandler->addUniform(kFragment_GrShaderFlag, kMat44f_GrSLType,
+                                                 kDefault_GrSLPrecision, "ColorXform",
+                                                 &fXformMatrix);
+        } else {
+            fXformMatrix = nullptr;
+        }
+    }
+
+    const char* getXformMatrix() const { return fXformMatrix; }
+
+private:
+    const char* fXformMatrix;
+};
+
+#endif