Create SkColorSpaceXform to handle color conversions

src/core/SkColorSpaceXform.h

Index: src/core/SkColorSpaceXform.h
diff --git a/src/core/SkColorSpaceXform.h b/src/core/SkColorSpaceXform.h
new file mode 100644
index 0000000000000000000000000000000000000000..8e58f0f42e40f5b10958602553411d0b22dd6364
--- /dev/null
+++ b/src/core/SkColorSpaceXform.h
@@ -0,0 +1,58 @@
+/*
+ * 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 SkColorSpaceXform_DEFINED
+#define SkColorSpaceXform_DEFINED
+
+#include "SkColorSpace.h"
+
+class SkColorSpaceXform {
+public:
+
+    enum Op {
+        kSrcToLinear_Op,         // Apply src gamma
+        kSrcToLinearDstGamut_Op, // Apply src gamma and matrix
+        kSrcToDst_Op,            // Apply src gamma, matrix, and dst gamma
+    };
+
+    /**
+     *  Create an object to handle color space conversions.
+     *
+     *  @param srcSpace The encoded color space.  This is required if the conversion op
+     *                  will begin in the encoded gamut.  Otherwise it may be nullptr.
+     *  @param dstSpace The destination color space.  This is required if the conversion op
+     *                  will finish in the destination gamut.  Otherwise it may be nullptr.
+     *  @param op       Indicates the start and end point of the conversion.
+     *
+     */
+    static SkColorSpaceXform* New(sk_sp<SkColorSpace> srcSpace, sk_sp<SkColorSpace> dstSpace,
+                                  Op op);
+
+    /**
+     *  Apply the color conversion to a src buffer, storing the output in the dst buffer.

[Brian Osman, 2016/05/05 13:29:44]

Should probably document that this assumes (requires) RGBA_8888 buffers.

[msarett, 2016/05/05 15:49:05]

Yes you're right!

I think it makes sense to start with RGBA_8888->F16, but we could always add
additional functions here (ex: RGBA_8888->10_10_10).  In that case, we might
want a more descriptive name as well (maybe apply8888ToF16 or something).

+     */
+    virtual void apply(void* dst, const void* src, const SkISize& size, size_t dstRowBytes,
+                       size_t srcRowBytes) const = 0;
+
+    virtual ~SkColorSpaceXform() {}
+};
+
+class SkGammaByValueXform : public SkColorSpaceXform {
+public:
+
+    void apply(void* dst, const void* src, const SkISize& size, size_t dstRowBytes,
+               size_t srcRowBytes) const override;
+
+private:
+    SkGammaByValueXform(const SkFloat3& gammas);
+
+    const SkFloat3 fGammas;
+
+    friend class SkColorSpaceXform;
+};
+
+#endif