Add a class representing texture swizzle.

src/effects/SkTableColorFilter.cpp

Index: src/effects/SkTableColorFilter.cpp
diff --git a/src/effects/SkTableColorFilter.cpp b/src/effects/SkTableColorFilter.cpp
index 32617cd6fe4bc9a7c015aa7954e9af8a538a6cd0..d9c07e254cc60416f7c7287380e75b3cd8f83752 100644
--- a/src/effects/SkTableColorFilter.cpp
+++ b/src/effects/SkTableColorFilter.cpp
@@ -442,22 +442,22 @@ void GLColorTableEffect::emitCode(EmitArgs& args) {
     fragBuilder->codeAppendf("\t\t%s.a = ", args.fOutputColor);
     coord.printf("vec2(coord.a, %s.a)", yoffsets);
     fragBuilder->appendTextureLookup(args.fSamplers[0], coord.c_str());
-    fragBuilder->codeAppend(";\n");
+    fragBuilder->codeAppend(".a;\n");
 
     fragBuilder->codeAppendf("\t\t%s.r = ", args.fOutputColor);
     coord.printf("vec2(coord.r, %s.r)", yoffsets);
     fragBuilder->appendTextureLookup(args.fSamplers[0], coord.c_str());
-    fragBuilder->codeAppend(";\n");
+    fragBuilder->codeAppend(".a;\n");
 
     fragBuilder->codeAppendf("\t\t%s.g = ", args.fOutputColor);
     coord.printf("vec2(coord.g, %s.g)", yoffsets);
     fragBuilder->appendTextureLookup(args.fSamplers[0], coord.c_str());
-    fragBuilder->codeAppend(";\n");
+    fragBuilder->codeAppend(".a;\n");
 
     fragBuilder->codeAppendf("\t\t%s.b = ", args.fOutputColor);
     coord.printf("vec2(coord.b, %s.b)", yoffsets);
     fragBuilder->appendTextureLookup(args.fSamplers[0], coord.c_str());
-    fragBuilder->codeAppend(";\n");
+    fragBuilder->codeAppend(".a;\n");
 
     fragBuilder->codeAppendf("\t\t%s.rgb *= %s.a;\n", args.fOutputColor, args.fOutputColor);
 }
@@ -487,7 +487,7 @@ const GrFragmentProcessor* ColorTableEffect::Create(GrContext* context, SkBitmap
 
 ColorTableEffect::ColorTableEffect(GrTexture* texture, GrTextureStripAtlas* atlas, int row,
                                    unsigned flags)
-    : fTextureAccess(texture, "a")
+    : fTextureAccess(texture)
     , fFlags(flags)
     , fAtlas(atlas)
     , fRow(row) {