Add function for creating ASTC blitter

src/utils/SkTextureCompressor.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTextureCompressor.h"
 #include "SkTextureCompressor_ASTC.h"
 #include "SkTextureCompressor_LATC.h"
@@ skipping 104 matching lines @@
 }
 
 SkBlitter* CreateBlitterForFormat(int width, int height, void* compressedBuffer, Format format) {
     switch(format) {
         case kLATC_Format:
             return CreateLATCBlitter(width, height, compressedBuffer);
 
         case kR11_EAC_Format:
             return CreateR11EACBlitter(width, height, compressedBuffer);
 
+        case kASTC_12x12_Format:
+            return CreateASTCBlitter(width, height, compressedBuffer);
+
         default:
             return NULL;
     }
 
     return NULL;
 }
 
 }  // namespace SkTextureCompressor