Add a class representing texture swizzle.

src/gpu/glsl/GrGLSLTextureSampler.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLSLTextureSampler_DEFINED
 #define GrGLSLTextureSampler_DEFINED
 
 #include "GrShaderVar.h"
 #include "GrTextureAccess.h"
 #include "glsl/GrGLSLProgramDataManager.h"
 
 class GrGLSLTextureSampler {
 public:
     typedef GrGLSLProgramDataManager::UniformHandle UniformHandle;
     typedef SkTArray<GrGLSLTextureSampler> TextureSamplerArray;
 
     GrGLSLTextureSampler(UniformHandle uniform, const GrTextureAccess& access)
         : fSamplerUniform(uniform)
         , fConfig(access.getTexture()->config()) {
         SkASSERT(kUnknown_GrPixelConfig != fConfig);
-        memcpy(fSwizzle, access.getSwizzle(), 5);
     }
 
     GrPixelConfig config() const { return fConfig; }
-    // this is .abcd
-    const char* swizzle() const { return fSwizzle; }
 
 private:
     UniformHandle fSamplerUniform;
     GrPixelConfig fConfig;
-    char          fSwizzle[5];
 
     friend class GrGLSLShaderBuilder;
 };
 
 #endif