Make swizzling in read/write pixel copy code more generic

src/gpu/GrSwizzle.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 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
     assignment operator. That could be relaxed. */
 class GrSwizzle {
 public:
     GrSwizzle() { *this = RGBA(); }
 
     GrSwizzle(const GrSwizzle& that) { *this = that; }
 
@@ skipping 54 matching lines @@
     static const GrSwizzle& RRRR() {
         static GrSwizzle gRRRR("rrrr");
         return gRRRR;
     }
 
     static const GrSwizzle& BGRA() {
         static GrSwizzle gBGRA("bgra");
         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;
 
     static int CharToIdx(char c) {
         switch (c) {
             case 'r':
                 return (GrColor_SHIFT_R / 8);
             case 'g':
                 return (GrColor_SHIFT_G / 8);
@@ skipping 30 matching lines @@
                       (CharToIdx(fSwiz[2]) << 4) | (CharToIdx(fSwiz[3]) << 6));
     }
 
     uint32_t* asUIntPtr() { return SkTCast<uint32_t*>(fSwiz); }
     uint32_t asUInt() const { return *SkTCast<const uint32_t*>(fSwiz); }
 
     GR_STATIC_ASSERT(sizeof(char[4]) == sizeof(uint32_t));
 };
 
 #endif