Move SkColorChannel into SkColor

By making it in a more common header, this enum can be reused by the
SkDisplacementMapEffect.

Bug: skia:9280
Change-Id: Ia8352e0530f915cdad659c657bd86710226582b6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/230118
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Auto-Submit: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>

include/core/SkColor.h

@@ -218,6 +218,18 @@ SK_API SkPMColor SkPreMultiplyARGB(U8CPU a, U8CPU r, U8CPU g, U8CPU b);
 */
 SK_API SkPMColor SkPreMultiplyColor(SkColor c);
 
+/** \enum SkColorChannel
+    Describes different color channels one can manipulate
+*/
+enum class SkColorChannel {
+    kR,  // the red channel
+    kG,  // the green channel
+    kB,  // the blue channel
+    kA,  // the alpha channel
+
+    kLastEnum = kA,
+};
+
 /** \struct SkRGBA4f
     RGBA color value, holding four floating point components. Color components are always in
     a known order. kAT determines if the SkRGBA4f's R, G, and B components are premultiplied

include/core/SkYUVAIndex.h

@@ -8,20 +8,9 @@
 #ifndef SkYUVAIndex_DEFINED
 #define SkYUVAIndex_DEFINED
 
+#include "include/core/SkColor.h"
 #include "include/core/SkTypes.h"
 
-/** \enum SkColorChannel
-    Describes different color channels one can manipulate
-*/
-enum class SkColorChannel {
-    kR,  // the red channel
-    kG,  // the green channel
-    kB,  // the blue channel
-    kA,  // the alpha channel
-
-    kLastEnum = kA,
-};
-
 /** \struct SkYUVAIndex
     Describes from which image source and which channel to read each individual YUVA plane.