Make swizzling in read/write pixel copy code more generic

src/gpu/GrSwizzle.h

Index: src/gpu/GrSwizzle.h
diff --git a/src/gpu/GrSwizzle.h b/src/gpu/GrSwizzle.h
index 48748803ddb2d3daceea66233d7a0d238ff61b38..c2288b2fe41863053b38cba236d2792a3bf31bfb 100644
--- a/src/gpu/GrSwizzle.h
+++ b/src/gpu/GrSwizzle.h
@@ -8,8 +8,8 @@
 #ifndef GrSwizzle_DEFINED
 #define GrSwizzle_DEFINED
 
-#include "GrTypes.h"
 #include "GrColor.h"
+#include "SkRandom.h"
 
 /** Represents a rgba swizzle. It can be converted either into a string or a eight bit int.
     Currently there is no way to specify an arbitrary swizzle, just some static swizzles and an
@@ -84,6 +84,22 @@ public:
         return gBGRA;
     }
 
+    static const GrSwizzle& CreateRandom(SkRandom* random) {
+        switch (random->nextU() % 4) {
+            case 0:
+                return RGBA();
+            case 1:
+                return BGRA();
+            case 2:
+                return RRRR();
+            case 3:
+                return AAAA();
+            default:
+                SkFAIL("Mod is broken?!?");
+                return RGBA();
+        }
+    }
+
 private:
     char fSwiz[5];
     uint8_t fKey;